diff options
Diffstat (limited to 'open_issues')
| -rw-r--r-- | open_issues/anatomy_of_a_hurd_system.mdwn | 111 | ||||
| -rw-r--r-- | open_issues/fakeroot_eagain.mdwn | 216 | ||||
| -rw-r--r-- | open_issues/gnumach_memory_management.mdwn | 49 | ||||
| -rw-r--r-- | open_issues/libpthread.mdwn | 92 | ||||
| -rw-r--r-- | open_issues/netstat.mdwn | 34 | ||||
| -rw-r--r-- | open_issues/performance.mdwn | 103 | ||||
| -rw-r--r-- | open_issues/robustness.mdwn | 65 | ||||
| -rw-r--r-- | open_issues/select.mdwn | 128 |
8 files changed, 783 insertions, 15 deletions
diff --git a/open_issues/anatomy_of_a_hurd_system.mdwn b/open_issues/anatomy_of_a_hurd_system.mdwn index 99ef170b..3e585876 100644 --- a/open_issues/anatomy_of_a_hurd_system.mdwn +++ b/open_issues/anatomy_of_a_hurd_system.mdwn @@ -13,7 +13,10 @@ License|/fdl]]."]]"""]] A bunch of this should also be covered in other (introductionary) material, like Bushnell's Hurd paper. All this should be unfied and streamlined. -IRC, freenode, #hurd, 2011-03-08: +[[!toc]] + + +# IRC, freenode, #hurd, 2011-03-08 <foocraft> I've a question on what are the "units" in the hurd project, if you were to divide them into units if they aren't, and what are the @@ -38,9 +41,8 @@ IRC, freenode, #hurd, 2011-03-08: <antrik> no <antrik> servers often depend on other servers for certain functionality ---- -IRC, freenode, #hurd, 2011-03-12: +# IRC, freenode, #hurd, 2011-03-12 <dEhiN> when mach first starts up, does it have some basic i/o or fs functionality built into it to start up the initial hurd translators? @@ -72,24 +74,24 @@ IRC, freenode, #hurd, 2011-03-12: <antrik> it also does some bootstrapping work during startup, to bring the rest of the system up ---- + +# Source Code Documentation Provide a cross-linked sources documentation, including generated files, like RPC stubs. * <http://www.gnu.org/software/global/> ---- -[[Hurd_101]]. +# [[Hurd_101]] + ---- +# [[hurd/IO_path]] -More stuff like [[hurd/IO_path]]. +Need more stuff like that. ---- -IRC, freenode, #hurd, 2011-10-18: +# IRC, freenode, #hurd, 2011-10-18 <frhodes> what happens @ boot. and which translators are started in what order? @@ -97,9 +99,8 @@ IRC, freenode, #hurd, 2011-10-18: ext2; ext2 starts exec; ext2 execs a few other servers; ext2 execs init. from there on, it's just standard UNIX stuff ---- -IRC, OFTC, #debian-hurd, 2011-11-02: +# IRC, OFTC, #debian-hurd, 2011-11-02 <sekon_> is __dir_lookup a RPC ?? <sekon_> where can i find the source of __dir_lookup ?? @@ -123,9 +124,8 @@ IRC, OFTC, #debian-hurd, 2011-11-02: <tschwinge> sekon_: This may help a bit: http://www.gnu.org/software/hurd/hurd/hurd_hacking_guide.html ---- -IRC, freenode, #hurd, 2012-01-08: +# IRC, freenode, #hurd, 2012-01-08 <abique> can you tell me how is done in hurd: "ls | grep x" ? <abique> in bash @@ -187,7 +187,8 @@ IRC, freenode, #hurd, 2012-01-08: <antrik> that's probably the most fundamental design feature of the Hurd <antrik> (all filesystem operations actually, not only lookups) -IRC, freenode, #hurd, 2012-01-09: + +## IRC, freenode, #hurd, 2012-01-09 <braunr> youpi: are you sure cthreads are M:N ? i'm almost sure they're 1:1 <braunr> and no modern OS is a right place for any thread userspace @@ -266,3 +267,83 @@ IRC, freenode, #hurd, 2012-01-09: <youpi> they help only when the threads are living <braunr> ok <youpi> now as I said I don't have to talk much more, I have to leave :) + + +# IRC, freenode, #hurd, 2012-12-06 + + <braunr> spiderweb: have you read + http://www.gnu.org/software/hurd/hurd-paper.html ? + <spiderweb> I'll have a look. + <braunr> and also the beginning of + http://ftp.sceen.net/mach/mach_a_new_kernel_foundation_for_unix_development.pdf + <braunr> these two should provide a good look at the big picture the hurd + attemtps to achieve + <Tekk_> I can't help but wonder though, what advantages were really + achieved with early mach? + <Tekk_> weren't they just running a monolithic unix server like osx does? + <braunr> most mach-based systems were + <braunr> but thanks to that, they could provide advanced features over + other well established unix systems + <braunr> while also being compatible + <Tekk_> so basically it was just an ease of development thing + <braunr> well that's what mach aimed at being + <braunr> same for the hurd + <braunr> making things easy + <Tekk_> but as a side effect hurd actually delivers on the advantages of + microkernels aside from that, but the older systems wouldn't, correct? + <braunr> that's how there could be network file systems in very short time + and very scarce resources (i.e. developers working on it), while on other + systems it required a lot more to accomplish that + <braunr> no, it's not a side effect of the microkernel + <braunr> the hurd retains and extends the concept of flexibility introduced + by mach + <Tekk_> the improved stability, etc. isn't a side effect of being able to + restart generally thought of as system-critical processes? + <braunr> no + <braunr> you can't restart system critical processes on the hurd either + <braunr> that's one feature of minix, and they worked hard on it + <Tekk_> ah, okay. so that's currently just the domain of minix + <Tekk_> okay + <Tekk_> spiderweb: well, there's 1 advantage of minix for you :P + <braunr> the main idea of mach is to make it easy to extend unix + <braunr> without having hundreds of system calls + <braunr> the hurd keeps that and extends it by making many operations + unprivileged + <braunr> you don't need special code for kernel modules any more + <braunr> it's easy + <braunr> you don't need special code to handle suid bits and other ugly + similar hacks, + <braunr> it's easy + <braunr> you don't need fuse + <braunr> easy + <braunr> etc.. + + +# IRC, freenode, #hurd, 2012-12-06 + + <spiderweb> what is the #1 feature that distinguished hurd from other + operating systems. the concept of translators. (will read more when I get + more time). + <braunr> yes, translators + <braunr> using the VFS as a service directory + <braunr> and the VFS permissions to control access to those services + + +# IRC, freenode, #hurd, 2012-12-10 + + <spiderweb> I want to work on hurd, but I think I'm going to start with + minix, I own the minix book 3rd ed. it seems like a good intro to + operating systems in general. like I don't even know what a semaphore is + yet. + <braunr> well, enjoy learning :) + <spiderweb> once I finish that book, what reading do you guys recommend? + <spiderweb> other than the wiki + <braunr> i wouldn't recommend starting with a book that focuses on one + operating system anyway + <braunr> you tend to think in terms of what is done in that specific + implementation and compare everything else to that + <braunr> tannenbaum is not only the main author or minix, but also the one + of the book http://en.wikipedia.org/wiki/Modern_Operating_Systems + <braunr> + http://en.wikipedia.org/wiki/List_of_important_publications_in_computer_science#Operating_systems + should be a pretty good list :) diff --git a/open_issues/fakeroot_eagain.mdwn b/open_issues/fakeroot_eagain.mdwn new file mode 100644 index 00000000..6b684a04 --- /dev/null +++ b/open_issues/fakeroot_eagain.mdwn @@ -0,0 +1,216 @@ +[[!meta copyright="Copyright © 2012 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_glibc open_issue_porting]] + + +# IRC, freenode, #hurd, 2012-12-05 + + <braunr> rbraun 18813 R 2hrs ln -sf ../af_ZA/LC_NUMERIC + debian/locales-all/usr/lib/locale/en_BW/LC_NUMERIC + <braunr> when building glibc + <braunr> is this a known issue ? + <tschwinge> braunr: No. Can you get a backtrace? + <braunr> tschwinge: with gdb you mean ? + <tschwinge> Yes. If you have any debugging symbols (glibc?). + <braunr> or the build log leading to that ? + <braunr> ok, i will next time i have it + <tschwinge> OK. + <braunr> (i regularly had it when working on the pthreads port) + <braunr> tschwinge: + http://www.sceen.net/~rbraun/hurd_glibc_build_deadlock_trace + <braunr> youpi: ^ + <youpi> Mmm, there's not so much we can do about this one + <braunr> youpi: what do you mean ? + <youpi> the problem is that it's really a reentrency issue of the libc + locale + <youpi> it would happen just the same on linux + <braunr> sure + <braunr> but hat doesn't mean we can't report and/or fix it :) + <youpi> (the _nl_state_lock) + <braunr> do you have any workaround in mind ? + <youpi> no + <youpi> actually that's what I meant by "there's not so much we can do + about this" + <braunr> ok + <youpi> because it's a bad interaction between libfakeroot and glibc + <youpi> glibc believe fxtstat64 would never call locale functions + <youpi> but with libfakeroot it does + <braunr> i see + <youpi> only because we get an EAGAIN here + <braunr> but hm, doesn't it happen on linux ? + <youpi> EAGAIN doesn't happen on linux for fxstat64, no :) + <braunr> why does it happen on the hurd ? + <youpi> I mean for fakeroot stuff + <youpi> probably because fakeroot uses socket functions + <youpi> for which we probably don't properly handleEAGAIN + <youpi> I've already seen such kind of issue + <youpi> in buildd failures + <braunr> ok + <youpi> (so the actual bug here is EAGAIN + <youpi> ) + <braunr> yes, so we can do something about it + <braunr> worth a look + <pinotree> (implement sysv semaphores) + <youpi> pinotree: if we could also solve all these buildd EAGAIN issues + that'd be nice :) + <braunr> that EAGAIN error might also be what makes exim behave badly and + loop forever + <youpi> possibly + <braunr> i've updated the trace with debugging symbols + <braunr> it fails on connect + <pinotree> like http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=563342 ? + <braunr> it's EAGAIN, not ECONNREFUSED + <pinotree> ah ok + <braunr> might be an error in tcp_v4_get_port + + +## IRC, freenode, #hurd, 2012-12-06 + + <braunr> hmm, tcp_v4_get_port sometimes fails indeed + <gnu_srs> braunr: may I ask how you found out, adding print statements in + pfinet, or? + <braunr> yes + <gnu_srs> OK, so that's the only (easy) way to debug. + <braunr> that's the last resort + <braunr> gdb is easy too + <braunr> i could have added a breakpoint too + <braunr> but i didn't want to block pfinet while i was away + <braunr> is it possible to force the use of fakeroot-tcp on linux ? + <braunr> the problem seems to be that fakeroot doesn't close the sockets + that it connected to faked-tcp + <braunr> which, at some point, exhauts the port space + <pinotree> braunr: sure + <pinotree> change the fakeroot dpkg alternative + <braunr> ok + <pinotree> calling it explicitly `fakeroot-tcp command` or + `dpkg-buildpackage -rfakeroot-tcp ...` should work too + <braunr> fakeroot-tcp looks really evil :p + <braunr> hum, i don't see any faked-tcp process on linux :/ + <pinotree> not even with `fakeroot-tcp bash -c "sleep 10"`? + <braunr> pinotree: now yes + <braunr> but, does it mean faked-tcp is started for *each* process loading + fakeroot-tcp ? + <braunr> (the lib i mean) + <pinotree> i think so + <braunr> well the hurd doesn't seem to do that at all + <braunr> or maybe it does and i don't see it + <braunr> the stale faked-tcp processes could be those that failed something + only + <pinotree> yes, there's also that issue: sometimes there are stake + faked-tcp processes + <braunr> hum no, i see one faked-tcp that consumes cpu when building glibc + <pinotree> *stale + <braunr> it's the same process for all commands + <pinotree> <braunr> but, does it mean faked-tcp is started for *each* + process loading fakeroot-tcp ? + <pinotree> → everytime you start fakeroot, there's a new faked-xxx for it + <braunr> it doesn't look that way + <braunr> again, on the hurd, i see one faked-tcp, consuming cpu while + building so i assume it services libfakeroot-tcp requests + <pinotree> yes + <braunr> which means i probably won't reproduce the problem on linux + <pinotree> it serves that fakeroot under which the binary(-arch) target is + run + <braunr> or perhaps it's the normal fakeroot-tcp behaviour on sid + <braunr> pinotree: a faked-tcp that is started for each command invocation + will implicitely make the network stack close all its sockets when + exiting + <braunr> pinotree: as our fakeroot-tcp uses the same instance of faked-tcp, + it's a lot more likely to exhaust the port space + <pinotree> i see + <braunr> i'll try on sid and see how it behaves + <braunr> pinotree: on the other hand, forking so many processes at each + command invocation may make exec leak a lot :p + <braunr> or rather, a lot more + <braunr> (or maybe not, since it leaks only in some cases) + +[[exec_leak]]. + + <braunr> pinotree: actually, the behaviour under linux is the same with the + alternative correctly set, whereas faked-tcp is restarted (if used at + all) with -rfakeroot-tcp + <braunr> hm no, even that isn't true + <braunr> grr + <braunr> pinotree: i think i found a handy workaround for fakeroot + <braunr> pinotree: the range of local ports in our networking stack is a + lot more limited than what is configured in current systems + <braunr> by extending it, i can now build glibc \o/ + <pinotree> braunr: what are the current ours and the usual one? + <braunr> see pfinet/linux-src/net/ipv4/tcp_ipv4.c + <braunr> the modern ones are the ones suggested in the comment + <braunr> sysctl_local_port_range is the symbol storing the range + <pinotree> i see + <pinotree> what's the current range on linux? + <braunr> 20:44 < braunr> the modern ones are the ones suggested in the + comment + <pinotree> i see + <braunr> $ cat /proc/sys/net/ipv4/ip_local_port_range + <braunr> 32768 61000 + <braunr> so, i'm not sure why we have the problem, since even on linux, + netstat doesn't show open bound ports, but it does help + <braunr> the fact faked-tcp can remain after its use is more problematic + <pinotree> (maybe pfinet could grow a (startup-only?) option to change it, + similar to that sysctl) + <braunr> but it can also stems from the same issue gnu_srs found about + closed sockets that haven't been shut down + <braunr> perhaps + <braunr> but i don't see the point actually + <braunr> we could simply change the values in the code + + <braunr> youpi: first, in pfinet, i increased the range of local ports to + reduce the likeliness of port space exhaustion + <braunr> so we should get a lot less EAGAIN after that + <braunr> (i've not committed any of those changes) + <youpi> range of local ports? + <braunr> see pfinet/linux-src/net/ipv4/tcp_ipv4.c, tcp_v4_get_port function + and sysctl_local_port_range array + <youpi> oh + <braunr> EAGAIN is caused by tcp_v4_get_port failing at + <braunr> /* Exhausted local port range during search? */ + <braunr> if (remaining <= 0) + <braunr> goto fail; + <youpi> interesting + <youpi> so it's not a hurd bug after all + <youpi> just a problem in fakeroot eating a lot of ports + <braunr> maybe because of the same issue gnu_srs worked on (bad socket + close when no clean shutdown) + <braunr> maybe, maybe not + <braunr> but increasing the range is effective + <braunr> and i compared with what linux does today, which is exactly what + is in the comment above sysctl_local_port_range + <braunr> so it looks safe + <youpi> so that means that the pfinet just uses ports 1024- 4999 for + auto-allocated ports? + <braunr> i guess so + <youpi> the linux pfinet I meant + <braunr> i haven't checked the whole code but it looks that way + <youpi> ./sysctl_net_ipv4.c:static int ip_local_port_range_min[] = { 1, 1 + }; + <youpi> ./sysctl_net_ipv4.c:static int ip_local_port_range_max[] = { 65535, + 65535 }; + <youpi> looks like they have increased it since then :) + <braunr> hum :) + <braunr> $ cat /proc/sys/net/ipv4/ip_local_port_range + <braunr> 32768 61000 + <youpi> yep, same here + <youpi> ./inet_connection_sock.c: .range = { 32768, 61000 }, + <youpi> so there are two things apparently + <youpi> but linux now defaults to 32k-61k + <youpi> braunr: please just push the port range upgrade to 32Ki-61K + <braunr> ok, will do + <youpi> there's not reason not to do it + + +## IRC, freenode, #hurd, 2012-12-11 + + <braunr> youpi: at least, i haven't had any failure building eglibc since + the port range patch + <youpi> good :) diff --git a/open_issues/gnumach_memory_management.mdwn b/open_issues/gnumach_memory_management.mdwn index 9feb30c8..e5e9d2c5 100644 --- a/open_issues/gnumach_memory_management.mdwn +++ b/open_issues/gnumach_memory_management.mdwn @@ -2133,3 +2133,52 @@ There is a [[!FF_project 266]][[!tag bounty]] on this task. <braunr> do you want to review ? <youpi> I don't think there is any need to <braunr> ok + + +# IRC, freenode, #hurd, 2012-12-08 + + <mcsim> braunr: hi. Do I understand correct that merely the same technique + is used in linux to determine the slab where, the object to be freed, + resides? + <braunr> yes but it's faster on linux since it uses a direct mapping of + physical memory + <braunr> it just has to shift the virtual address to obtain the physical + one, whereas x15 has to walk the pages tables + <braunr> of course it only works for kmalloc, vmalloc is entirely different + <mcsim> btw, is there sense to use some kind of B-tree instead of AVL to + decrease number of cache misses? AFAIK, in modern processors size of L1 + cache line is at least 64 bytes, so in one node we can put at least 4 + leafs (key + pointer to data) making search faster. + <braunr> that would be a b-tree + <braunr> and yes, red-black trees were actually developed based on + properties observed on b-trees + <braunr> but increasing the size of the nodes also increases memory + overhead + <braunr> and code complexity + <braunr> that's why i have a radix trees for cases where there are a large + number of entries with keys close to each other :) + <braunr> a radix-tree is basically a b-tree using the bits of the key as + indexes in the various arrays it walks instead of comparing keys to each + other + <braunr> the original avl tree used in my slab allocator was intended to + reduce the average height of the tree (avl is better for that) + <braunr> avl trees are more suited for cases where there are more lookups + than inserts/deletions + <braunr> they make the tree "flatter" but the maximum complexity of + operations that change the tree is 2log2(n), since rebalancing the tree + can make the algorithm reach back to the tree root + <braunr> red-black trees have slightly bigger heights but insertions are + limited to 2 rotations and deletions to 3 + <mcsim> there should be not much lookups in slab allocators + <braunr> which explains why they're more generally found in generic + containers + <mcsim> or do I misunderstand something? + <braunr> well, there is a lookup for each free() + <braunr> whereas there are insertions/deletions when a slab becomes + non-empty/empty + <mcsim> I see + <braunr> so it was very efficient for caches of small objects, where slabs + have many of them + <braunr> also, i wrote the implementation in userspace, without + functionality pmap provides (although i could have emulated it + afterwards) diff --git a/open_issues/libpthread.mdwn b/open_issues/libpthread.mdwn index 81f1a382..befc1378 100644 --- a/open_issues/libpthread.mdwn +++ b/open_issues/libpthread.mdwn @@ -1234,3 +1234,95 @@ There is a [[!FF_project 275]][[!tag bounty]] on this task. of a "message server" à la dmesg [[translator_stdout_stderr]]. + + +### IRC, freenode, #hurd, 2012-12-10 + + <youpi> braunr: unable to adjust libports thread priority: (ipc/send) + invalid destination port + <youpi> I'll see what package brought that + <youpi> (that was on a buildd) + <braunr> wow + <youpi> mkvtoolnix_5.9.0-1: + <pinotree> shouldn't that code be done in pthreads and then using such + pthread api? :p + <braunr> pinotree: you've already asked that question :p + <pinotree> i know :p + <braunr> the semantics of pthreads are larger than what we need, so that + will be done "later" + <braunr> but this error shouldn't happen + <braunr> it looks more like a random mach bug + <braunr> youpi: anything else on the console ? + <youpi> nope + <braunr> i'll add traces to know which step causes the error + + +## IRC, freenode, #hurd, 2012-12-05 + + <braunr> tschwinge: i'm currently working on a few easy bugs and i have + planned improvements for libpthreads soon + <pinotree> wotwot, which ones? + <braunr> pinotree: first, fixing pthread_cond_timedwait (and everything + timedsomething actually) + <braunr> pinotree: then, fixing cancellation + <braunr> pinotree: and last but not least, optimizing thread wakeup + <braunr> i also want to try replacing spin locks and see if it does what i + expect + <pinotree> which fixes do you plan applying to cond_timedwait? + <braunr> see sysdeps/generic/pt-cond-timedwait.c + <braunr> the FIXME comment + <pinotree> ah that + <braunr> well that's important :) + <braunr> did you have something else in mind ? + <pinotree> hm, __pthread_timedblock... do you plan fixing directly there? i + remember having seem something related to that (but not on conditions), + but wasn't able to see further + <braunr> it has the same issue + <braunr> i don't remember the details, but i wrote a cthreads version that + does it right + <braunr> in the io_select_timeout branch + <braunr> see + http://git.savannah.gnu.org/cgit/hurd/hurd.git/tree/libthreads/cancel-cond.c?h=rbraun/select_timeout + for example + * pinotree looks + <braunr> what matters is the msg_delivered member used to synchronize + sleeper and waker + <braunr> the waker code is in + http://git.savannah.gnu.org/cgit/hurd/hurd.git/tree/libthreads/cprocs.c?h=rbraun/select_timeout + <pinotree> never seen cthreads' code before :) + <braunr> soon you shouldn't have any more reason to :p + <pinotree> ah, so basically the cthread version of the pthread cleanup + stack + cancelation (ie the cancel hook) broadcasts the condition + <braunr> yes + <pinotree> so a similar fix would be needed in all the places using + __pthread_timedblock, that is conditions and mutexes + <braunr> and that's what's missing in glibc that prevents deploying a + pthreads based hurd currently + <braunr> no that's unrelated + <pinotree> ok + <braunr> the problem is how __pthread_block/__pthread_timedblock is + synchronized with __pthread_wakeup + <braunr> libpthreads does exactly the same thing as cthreads for that, + i.e. use messages + <braunr> but the message alone isn't enough, since, as explained in the + FIXME comment, it can arrive too late + <braunr> it's not a problem for __pthread_block because this function can + only resume after receiving a message + <braunr> but it's a problem for __pthread_timedblock which can resume + because of a timeout + <braunr> my solution is to add a flag that says whether a message was + actually sent, and lock around sending the message, so that the thread + resume can accurately tell in which state it is + <braunr> and drain the message queue if needed + <pinotree> i see, race between the "i stop blocking because of timeout" and + "i stop because i got a message" with the actual check for the real cause + <braunr> locking around mach_msg may seem overkill but it's not in + practice, since there can only be one message at most in the message + queue + <braunr> and i checked that in practice by limiting the message queue size + and check for such errors + <braunr> but again, it would be far better with mutexes only, and no spin + locks + <braunr> i wondered for a long time why the load average was so high on the + hurd under even "light" loads + <braunr> now i know :) diff --git a/open_issues/netstat.mdwn b/open_issues/netstat.mdwn new file mode 100644 index 00000000..b575ea7f --- /dev/null +++ b/open_issues/netstat.mdwn @@ -0,0 +1,34 @@ +[[!meta copyright="Copyright © 2012 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_glibc open_issue_hurd open_issue_porting]] + + +# IRC, freenode, #hurd, 2012-12-06 + + <braunr> we need a netstat command + <pinotree> wouldn't that require rpcs and notifications in pfinet to get + info on the known sockets? + <braunr> depends on the interface + <braunr> netstat currently uses /proc/net/* so that's out of the question + <braunr> but a bsd netstat using ioctls could do the job + <braunr> i'm not sure if it's done that way + <braunr> i don't see why it would require notifications though + <pinotree> if add such rpcs to pfinet, you could show the sockets in procfs + <braunr> yes + <braunr> that's the clean way :p + <braunr> but why notifications ? + <pinotree> to get changes on data of sockets (status change, i/o activity, + etc) + <pinotree> (possibly i'm forgetting some already there features to know + that) + <braunr> the socket state is centralized in pfinet + <braunr> netstat polls it + <braunr> (or asks it once) diff --git a/open_issues/performance.mdwn b/open_issues/performance.mdwn index 8147e5eb..ae05e128 100644 --- a/open_issues/performance.mdwn +++ b/open_issues/performance.mdwn @@ -83,6 +83,109 @@ call|/glibc/fork]]'s case. <antrik> ouch +## [[!message-id "20121202101508.GA30541@mail.sceen.net"]] + + +## IRC, freenode, #hurd, 2012-12-04 + + <damo22> why do some people think hurd is slow? i find it works well even + under heavy load inside a virtual machine + <braunr> damo22: the virtual machine actually assists the hurd a lot :p + <braunr> but even with that, the hurd is a slow system + <damo22> i would have thought it would have the potential to be very fast, + considering the model of the kernel + <braunr> the design implies by definition more overhead, but the true cause + is more than 15 years without optimization on the core components + <braunr> how so ? + <damo22> since there are less layers of code between the hardware bare + metal and the application that users run + <braunr> how so ? :) + <braunr> it's the contrary actually + <damo22> VFS -> IPC -> scheduler -> device drivers -> hardware + <damo22> that is monolithic + <braunr> well, it's not really meaningful + <braunr> and i'd say the same applies for a microkernel system + <damo22> if the application can talk directly to hardware through the + kernel its almost like plugging directly into the hardware + <braunr> you never talk directly to hardware + <braunr> you talk to servers instead of the kernel + <damo22> ah + <braunr> consider monolithic kernel systems like systems with one big + server + <braunr> the kernel + <braunr> whereas a multiserver system is a kernel and many servers + <braunr> you still need the VFS to identify your service (and thus your + server) + <braunr> you need much more IPC, since system calls are "replaced" with RPC + <braunr> the scheduler is basically the same + <damo22> okay + <braunr> device drivers are similar too, except they run in thread context + (which is usually a bit heavier) + <damo22> but you can do cool things like report when an interrupt line is + blocked + <braunr> and there are many context switches between all that + <braunr> you can do all that in a monolithic kernel too, and faster + <braunr> but it's far more elegant, and (when well done) easy to do on a + microkernel based system + <damo22> yes + <damo22> i like elegant, makes coding easier if you know the basics + <braunr> there are only two major differences between a monolilthic kernel + and a multiserver microkernel system + * damo22 listens + <braunr> 1/ independence of location (your resources could be anywhere) + <braunr> 2/ separation of address spaces (your servers have their own + addresses) + <damo22> wow + <braunr> these both imply additional layers of indirection, making the + system as a whole slower + <damo22> but it would be far more secure though i suspect + <braunr> yes + <braunr> and reliable + <braunr> that's why systems like qnx were usually adopted for critical + tasks + <damo22> security and reliability are very important, i would switch to the + hurd if it supported all the hardware i use + <braunr> so would i :) + <braunr> but performance matters too + <damo22> not to me + <braunr> it should :p + <braunr> it really does matter a lot in practice + <damo22> i mean, a 2x slowdown compared to linux would not affect me + <damo22> if it had all the benefits we mentioned above + <braunr> but the hurd is really slow for other reasons than its additional + layers of indrection unfortunately + <damo22> is it because of lack of optimisation in the core code? + <braunr> we're working on these issues, but it's not easy and takes a lot + of time :p + <damo22> like you said + <braunr> yes + <braunr> and also because of some fundamental design choices related to the + microkernel back in the 80s + <damo22> what about the darwin system + <damo22> it uses a mach kernel? + <braunr> yes + <damo22> what is stopping someone taking the MIT code from darwin and + creating a monster free OS + <braunr> what for ? + <damo22> because it already has hardware support + <damo22> and a mach kernel + <braunr> in kernel drivers ? + <damo22> it has kernel extensions + <damo22> you can do things like kextload module + <braunr> first, being a mach kernel doesn't make it compatible or even + easily usable with the hurd, the interfaces have evolved independantly + <braunr> and second, we really do want more stuff out of the kernel + <braunr> drivers in particular + <damo22> may i ask why you are very keen to have drivers out of kernel? + <braunr> for the same reason we want other system services out of the + kernel + <braunr> security, reliability, etc.. + <braunr> ease of debugging + <braunr> the ability to restart drivers separately, without restarting the + kernel + <damo22> i see + + # IRC, freenode, #hurd, 2012-09-13 {{$news/2011-q2#phoronix-3}}. diff --git a/open_issues/robustness.mdwn b/open_issues/robustness.mdwn index d32bd509..1f8aa0c6 100644 --- a/open_issues/robustness.mdwn +++ b/open_issues/robustness.mdwn @@ -62,3 +62,68 @@ License|/fdl]]."]]"""]] <antrik> well, I'm not aware of the Minix implementation working across reboots. the one I have in mind based on a generic session management infrastructure should though :-) + + +## IRC, freenode, #hurd, 2012-12-06 + + <Tekk_> out of curiosity, would it be possible to strap on a resurrection + server to hurd? + <Tekk_> in the future, that is + <braunr> sure + <Tekk_> cool :) + <braunr> but this requires things like persistence + <spiderweb> like a reincarnation server? + <braunr> it's a lot of works, with non negligible overhead + <Tekk_> spiderweb: yes, exactly. I didn't remember tanenbaum's wording on + that + <braunr> i'm pretty sure most people would be against that + <spiderweb> braunr: why so? + <Tekk_> it was actually the feature that convinced me that ukernels were a + good idea + <Tekk_> spiderweb: because then you need a process that keeps track of all + the other servers + <Tekk_> and they have to be replying to "useless" pings to see if they're + still alive + <braunr> spiderweb: the hurd community isn't looking for a system reliable + in critical environments + <braunr> just a general purpose system + <braunr> and persistence requires regular data saves + <braunr> it's expensive + <Tekk_> as well as that + <braunr> we already have performance problems because of the nature of the + system, adding more without really looking for the benefits is useless + <spiderweb> so you can't theoretically have both? + <braunr> persistence and performance ? + <braunr> it's hard + <Tekk_> spiderweb: you need to modify the other translators to be + persistent + <braunr> only the ones you care about actually + <braunr> but it's just better to make the critical servers very stable + <Tekk_> so it's not just turning on and off the reincarnation + <braunr> (there isn't that much code there) + <braunr> and the other servers restartable + <mcsim> braunr: I think that if there will be aim to make something like + resurrection server than it will be needed rewrite most servers to make + them stateless, isn't it? + <braunr> that's a lot easier and already works with non essential passive + translators + <Tekk_> mcsim: pretty much + <braunr> mcsim: only those you care about + <braunr> mcsim: the proc auth exec servers for example, perhaps the file + system servers that can act as root fs, but the others would simply be + restarted by the passive translator mechanism + <spiderweb> what about restarting device drivers, that would be simple + right? + <braunr> that's perfectly doable, yes + <spiderweb> (being an OS newbie) - it does seem to me that the whole + reincarnation server concept could quite possibly be a band aid. + <braunr> spiderweb: no it really works + <braunr> many systems do that actually + <braunr> let me give you a link + <braunr> + http://ftp.sceen.net/curios_improving_reliability_through_operating_system_structure.pdf + <braunr> it's a bit old, but there is a review of systems aiming at + resilience and how they achieve part of it + <spiderweb> neat, thanks + <braunr> actually it's not that old at all + <braunr> around 2007 diff --git a/open_issues/select.mdwn b/open_issues/select.mdwn index 12807e11..778af530 100644 --- a/open_issues/select.mdwn +++ b/open_issues/select.mdwn @@ -1503,6 +1503,134 @@ IRC, unknown channel, unknown date: [[Term_blocking]]. +# IRC, freenode, #hurd, 2012-12-05 + + <braunr> well if i'm unable to build my own packages, i'll send you the one + line patch i wrote that fixes select/poll for the case where there is + only one descriptor + <braunr> (the current code calls mach_msg twice, each time with the same + timeout, doubling the total wait time when there is no event) + + +## IRC, freenode, #hurd, 2012-12-06 + + <braunr> damn, my eglibc patch breaks select :x + <braunr> i guess i'll just simplify the code by using the same path for + both single fd and multiple fd calls + <braunr> at least, the patch does fix the case i wanted it to .. :) + <braunr> htop and ping act at the right regular interval + <braunr> my select patch is : + <braunr> /* Now wait for reply messages. */ + <braunr> - if (!err && got == 0) + <braunr> + if (!err && got == 0 && firstfd != -1 && firstfd != lastfd) + <braunr> basically, when there is a single fd, the code calls io_select + with a timeout + <braunr> and later calls mach_msg with the same timeout + <braunr> effectively making the maximum wait time twice what it should be + <pinotree> ouch + <braunr> which is why htop and ping are "laggy" + <braunr> and perhaps also why fakeroot is when building libc + <braunr> well + <braunr> when building packages + <braunr> my patch avoids entering the mach_msg call if there is only one fd + <braunr> (my failed attempt didn't have the firstfd != -1 check, leading to + the 0 fd case skipping mach_msg too, which is wrong since in that case + there is just no wait, making applications use select/poll for sleeping + consume all cpu) + + <braunr> the second is a fix in select (yet another) for the case where a + single fd is passed + <braunr> in which case there is one timeout directly passed in the + io_select call, but then yet another in the mach_msg call that waits for + replies + <braunr> this can account for the slowness of a bunch of select/poll users + + +## IRC, freenode, #hurd, 2012-12-07 + + <braunr> finally, my select patch works :) + + +## IRC, freenode, #hurd, 2012-12-08 + + <braunr> for those interested, i pushed my eglibc packages that include + this little select/poll timeout fix on my debian repository + <braunr> deb http://ftp.sceen.net/debian-hurd experimental/ + <braunr> reports are welcome, i'm especially interested in potential + regressions + + +## IRC, freenode, #hurd, 2012-12-10 + + <gnu_srs> I have verified your double timeout bug in hurdselect.c. + <gnu_srs> Since I'm also working on hurdselect I have a few questions + about where the timeouts in mach_msg and io_select are implemented. + <gnu_srs> Have a big problem to trace them down to actual code: mig magic + again? + <braunr> yes + <braunr> see hurd/io.defs, io_select includes a waittime timeout: + natural_t; parameter + <braunr> waittime is mig magic that tells the client side not to wait more + than the timeout + <braunr> and in _hurd_select, you can see these lines : + <braunr> err = __io_select (d[i].io_port, d[i].reply_port, + <braunr> /* Poll only if there's a single + descriptor. */ + <braunr> (firstfd == lastfd) ? to : 0, + <braunr> to being the timeout previously computed + <braunr> "to" + <braunr> and later, when waiting for replies : + <braunr> while ((msgerr = __mach_msg (&msg.head, + <braunr> MACH_RCV_MSG | options, + <braunr> 0, sizeof msg, portset, to, + <braunr> MACH_PORT_NULL)) == + MACH_MSG_SUCCESS) + <braunr> the same timeout is used + <braunr> hope it helps + <gnu_srs> Additional stuff on io-select question is at + http://paste.debian.net/215401/ + <gnu_srs> Sorry, should have posted it before you comment, but was + disturbed. + <braunr> 14:13 < braunr> waittime is mig magic that tells the client side + not to wait more than the timeout + <braunr> the waittime argument is a client argument only + <braunr> that's one of the main source of problems with select/poll, and + the one i fixed 6 months ago + <gnu_srs> so there is no relation to the third argument of the client call + and the third argument of the server code? + <braunr> no + <braunr> the 3rd argument at server side is undoubtedly the 4th at client + side here + <gnu_srs> but for the fourth argument there is? + <braunr> i think i've just answered that + <braunr> when in doubt, check the code generated by mig when building glibc + <gnu_srs> as I said before, I have verified the timeout bug you solved. + <gnu_srs> which code to look for RPC_*? + <braunr> should be easy to guess + <gnu_srs> is it the same with mach_msg()? No explicit usage of the timeout + there either. + <gnu_srs> in the code for the function I mean. + <braunr> gnu_srs: mach_msg is a low level system call + <braunr> see + http://www.gnu.org/software/hurd/gnumach-doc/Mach-Message-Call.html#Mach-Message-Call + <gnu_srs> found the definition of __io_select in: RPC_io_select.c, thanks. + <gnu_srs> so the client code to look for wrt RPC_ is in hurd/*.defs? what + about the gnumach/*/include/*.defs? + <gnu_srs> a final question: why use a timeout if there is a single FD for + the __io_select call, not when there are more than one? + <braunr> well, the code is obviously buggy, so don't expect me to justify + wrong code + <braunr> but i suppose the idea was : if there is only one fd, perform a + classical synchronous RPC, whereas if there are more use a heavyweight + portset and additional code to receive replies + + <youpi> exim4 didn't get fixed by the libc patch, unfortunately + <braunr> yes i noticed + <braunr> gdb can't attach correctly to exim, so it's probably something + completely different + <braunr> i'll try the non intrusive mode + + # See Also See also [[select_bogus_fd]] and [[select_vs_signals]]. |