diff options
| -rw-r--r-- | microkernel/mach/memory_object/discussion.mdwn | 43 | ||||
| -rw-r--r-- | open_issues/clock_gettime.mdwn | 30 | ||||
| -rw-r--r-- | open_issues/default_pager.mdwn | 28 | ||||
| -rw-r--r-- | open_issues/gnumach_memory_management.mdwn | 92 | ||||
| -rw-r--r-- | open_issues/mach_migrating_threads.mdwn | 15 | ||||
| -rw-r--r-- | open_issues/performance.mdwn | 8 | ||||
| -rw-r--r-- | open_issues/performance/degradation.mdwn | 14 | ||||
| -rw-r--r-- | open_issues/performance/ipc_virtual_copy.mdwn | 358 | ||||
| -rw-r--r-- | open_issues/time.mdwn | 16 | ||||
| -rw-r--r-- | open_issues/translators_set_up_by_untrusted_users.mdwn | 43 |
10 files changed, 644 insertions, 3 deletions
diff --git a/microkernel/mach/memory_object/discussion.mdwn b/microkernel/mach/memory_object/discussion.mdwn index a006429b..c874b255 100644 --- a/microkernel/mach/memory_object/discussion.mdwn +++ b/microkernel/mach/memory_object/discussion.mdwn @@ -10,7 +10,7 @@ License|/fdl]]."]]"""]] [[!tag open_issue_documentation open_issue_gnumach]] -IRC, freenode, #hurd, 2011-08-05 +IRC, freenode, #hurd, 2011-08-05: < neal> braunr: For instance, memory objects are great as they allow you to specify the mapping policy in user space. @@ -22,3 +22,44 @@ IRC, freenode, #hurd, 2011-08-05 < neal> I'm not sure what you mean by page cache lru appoximateion < braunr> the kernel eviction policy :) < neal> that's an implementation detail + +IRC, freenode, #hurd, 2011-09-05: + + <braunr> mach isn't a true modern microkernel, it handles a lot of + resources, such as high level virtual memory and cpu time + <braunr> for example, the page replacement mechanism can't be implemented + outside the kernel + <braunr> yet, it provides nothing to userspace server to easily allocate + resources on behalf of clients + <braunr> so, when a thread calls an RPC, the cpu time used to run that RPC + is accounted on the server task + <braunr> the hurd uses lots of external memory managers + +[[external_pager_mechanism]]. + + <braunr> but they can't decide how to interact with the page cache + <braunr> the kernel handles the page cache, and initiates the requests to + the pagers + <cjuner> braunr, why can't they decide that? + <braunr> because it's implemented in the kernel + <braunr> and there is nothing provided by mach to do that some other way + <slpz_> braunr: you probably already know this, but the problem with client + requests being accounted on behalf the server, is fixed in Mach with + Migrating Threads + +[[open_issues/mach_migrating_threads]]. + + <braunr> slpz_: migrating threads only fix the issue for the resources + managed by mach, not the external servers + <braunr> slpz_: but it's a (imo necessary) step to completely solve the + issue + <braunr> in addition to being a great feature for performance (lighter + context switchers, less state to track) + <braunr> it also helps priority inversion problems + <slpz_> braunr: I was referring just to cpu-time, but I agree with you an + interface change is needed for external pagers + <braunr> slpz_: servers in general, not necessarily pagers + <slpz_> as a way to mitigate the effect of Mach paging out to external + pagers, the folks at OSF implemented an "advisory pageout", so servers + are "warned" that they should start paging out, and can decide which + pages are going to be flushed by themselves diff --git a/open_issues/clock_gettime.mdwn b/open_issues/clock_gettime.mdwn index c06edc9b..5345ed6b 100644 --- a/open_issues/clock_gettime.mdwn +++ b/open_issues/clock_gettime.mdwn @@ -39,3 +39,33 @@ IRC, freenode, #hurd, 2011-08-26: < youpi> yes, it should work < braunr> sure < youpi> and that's the way I was considering implementing it + +IRC, freenode, #hurd, 2011-09-06: + + <pinotree> yeah, i had a draft of improved idea for also handling + nanoseconds + <tschwinge> pinotree: Ah, nice, I thought about nanoseconds as well. + <tschwinge> pinotree, youpi: This memory page is all-zero by default, + right? + <tschwinge> Can't we then say that its last int is a version code, and if + it is 0 (as it is now), we only have the normal mapped time field, if it + is 1, we also have the monotonic cliock and ns precision on address 8 and + 16 (or whatever)? + <tschwinge> In case that isn't your plan anyway. + <youpi> it's all-zero, yes + <tschwinge> Or, we say if a field is != 0 it is valid. + <youpi> making the last int a version code limits the size to one page + <youpi> I was thinking a field != 0 being valid is simpler + <youpi> but it's probably a problem too + <youpi> in that glibc usually caches whether interfaces are supported + <tschwinge> Wrap-around? + <youpi> for some clocks, it may be valid that the value is 0 + <youpi> wrap-around is another issue too + <tschwinge> Well, then we can do the version-field thing, but put it right + after the current time field (address 8, I think)? + <youpi> yes + <youpi> it's a bit ugly, but it's hidden behind the structure + <tschwinge> It's not too bad, I think. + <youpi> yes + <tschwinge> And it will forever be a witness of the evolving of this + map_time interface. :-) diff --git a/open_issues/default_pager.mdwn b/open_issues/default_pager.mdwn new file mode 100644 index 00000000..189179c6 --- /dev/null +++ b/open_issues/default_pager.mdwn @@ -0,0 +1,28 @@ +[[!meta copyright="Copyright © 2011 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_gnumach]] + +IRC, freenode, #hurd, 2011-08-31: + + <antrik> braunr: do you have any idea what could cause the paging errors + long before swap is exhausted? + <braunr> antrik: not really, but i know every project based on the mach vm + have rewritten their swap pager + <antrik> (and also I/O performance steadily dropping before that point is + reached?) + <antrik> hm + <braunr> there could too many things + <antrik> perhaps we could "borrow" from one of them? :-) + <braunr> map entry fragmentation for example + <braunr> the freebsd one is the only possible candidate + <braunr> uvm is too different + <braunr> dragonflybsd maybe, but it's very close to freebsd + <braunr> i didn't look at darwin/xnu diff --git a/open_issues/gnumach_memory_management.mdwn b/open_issues/gnumach_memory_management.mdwn index a728fc9d..1fe2f9be 100644 --- a/open_issues/gnumach_memory_management.mdwn +++ b/open_issues/gnumach_memory_management.mdwn @@ -1320,3 +1320,95 @@ There is a [[!FF_project 266]][[!tag bounty]] on this task. < braunr> i hope it helped you learn about memory allocation, virtual memory, gnu mach and the hurd in general :) < antrik> indeed :-) + + +# IRC, freenode, #hurd, 2011-09-06 + + [some performance testing] + <braunr> i'm not sure such long tests are relevant but let's assume balloc + is slower + <braunr> some tuning is needed here + <braunr> first, we can see that slab allocation occurs more often in balloc + than page allocation does in zalloc + <braunr> so yes, as slab allocation is slower (have you measured which part + actually is slow ? i guess it's the kmem_alloc call) + <braunr> the whole process gets a bit slower too + <mcsim> I used alloc_size = 4096 for zalloc + <braunr> i don't know what that is exactly + <braunr> but you can't hold 500 16 bytes buffers in a page so zalloc must + have had free pages around for that + <mcsim> I use kmem_alloc_wired + <braunr> if you have time, measure it, so that we know how much it accounts + for + <braunr> where are the results for dealloc ? + <mcsim> I can't give you result right now because internet works very + bad. But for first DEALLOC result are the same, exept some cases when it + takes balloc for more than 1000 ticks + <braunr> must be the transfer from the cpu layer to the slab layer + <mcsim> as to kmem_alloc_wired. I think zalloc uses this function too for + allocating objects in zone I test. + <braunr> mcsim: yes, but less frequently, which is why it's faster + <braunr> mcsim: another very important aspect that should be measured is + memory consumption, have you looked into that ? + <mcsim> I think that I made too little iterations in test SMALL + <mcsim> If I increase constant SMALL_TESTS will it be good enough? + <braunr> mcsim: i don't know, try both :) + <braunr> if you increase the number of iterations, balloc average time will + be lower than zalloc, but this doesn't remove the first long + initialization step on the allocated slab + <mcsim> SMALL_TESTS to 500, I mean + <braunr> i wonder if maintaining the slabs sorted through insertion sort is + what makes it slow + <mcsim> braunr: where do you sort slabs? I don't see this. + <braunr> mcsim: mem_cache_alloc_from_slab and its free counterpart + <braunr> mcsim: the mem_source stuff is useless in gnumach, you can remove + it and directly call the kmem_alloc/free functions + <mcsim> But I have to make special allocator for kernel map entries. + <braunr> ah right + <mcsim> btw. It turned out that 256 entries are not enough. + <braunr> that's weird + <braunr> i'll make a patch so that the mem_source code looks more like what + i have in x15 then + <braunr> about the results, i don't think the slab layer is that slow + <braunr> it's the cpu_pool_fill/drain functions that take time + <braunr> they preallocate many objects (64 for your objects size if i'm + right) at once + <braunr> mcsim: look at the first result page: some times, a number around + 8000 is printed + <braunr> the common time (ticks, whatever) for a single object is 120 + <braunr> 8132/120 is 67, close enough to the 64 value + <mcsim> I forgot about SMALL tests here are they: + http://paste.debian.net/128533/ (balloc) http://paste.debian.net/128534/ + (zalloc) + <mcsim> braunr: why do you divide 8132 by 120? + <braunr> mcsim: to see if it matches my assumption that the ~8000 number + matches the cpu_pool_fill call + <mcsim> braunr: I've got it + <braunr> mcsim: i'd be much interested in the dealloc results if you can + paste them too + <mcsim> dealloc: http://paste.debian.net/128589/ + http://paste.debian.net/128590/ + <braunr> mcsim: thanks + <mcsim> second dealloc: http://paste.debian.net/128591/ + http://paste.debian.net/128592/ + <braunr> mcsim: so the main conclusion i retain from your tests is that the + transfers from the cpu and the slab layers are what makes the new + allocator a bit slower + <mcsim> OPERATION_SMALL dealloc: http://paste.debian.net/128593/ + http://paste.debian.net/128594/ + <braunr> mcsim: what needs to be measured now is global memory usage + <mcsim> braunr: data from /proc/vmstat after kernel compilation will be + enough? + <braunr> mcsim: let me check + <braunr> mcsim: no it won't do, you need to measure kernel memory usage + <braunr> the best moment to measure it is right after zone_gc is called + <mcsim> Are there any facilities in gnumach for memory measurement? + <braunr> it's specific to the allocators + <braunr> just count the number of used pages + <braunr> after garbage collection, there should be no free page, so this + should be rather simple + <mcsim> ok + <mcsim> braunr: When I measure memory usage in balloc, what formula is + better cache->nr_slabs * cache->bufs_per_slab * cache->buf_size or + cache->nr_slabs * cache->slab_size? + <braunr> the latter diff --git a/open_issues/mach_migrating_threads.mdwn b/open_issues/mach_migrating_threads.mdwn new file mode 100644 index 00000000..5a70aac5 --- /dev/null +++ b/open_issues/mach_migrating_threads.mdwn @@ -0,0 +1,15 @@ +[[!meta copyright="Copyright © 2011 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_gnumach]] + +<http://www.brynosaurus.com/pub/os/thread-migrate.pdf> + + * [[microkernel/mach/memory_object/discussion]] diff --git a/open_issues/performance.mdwn b/open_issues/performance.mdwn index 54f3ce39..2fd34621 100644 --- a/open_issues/performance.mdwn +++ b/open_issues/performance.mdwn @@ -30,3 +30,11 @@ call|/glibc/fork]]'s case. --- * [[Degradation]] + + * [[fork]] + + * [[IPC_virtual_copy]] + + * [[microbenchmarks]] + + * [[microkernel_multi-server]] diff --git a/open_issues/performance/degradation.mdwn b/open_issues/performance/degradation.mdwn index 5db82e31..db759308 100644 --- a/open_issues/performance/degradation.mdwn +++ b/open_issues/performance/degradation.mdwn @@ -18,7 +18,7 @@ Thomas Schwinge) > tree, reboot, build it again (1st): back to 11 h. Remove build tree, build > it again (2nd): 12 h 40 min. Remove build tree, build it again (3rd): 15 h. -IRC, freenode, #hurd, 2011-07-23 +IRC, freenode, #hurd, 2011-07-23: < antrik> tschwinge: yes, the system definitely gets slower with time. after running for a couple of weeks, it needs at least twice as @@ -26,3 +26,15 @@ IRC, freenode, #hurd, 2011-07-23 < antrik> I don't know whether this is only related to swap usage, or there are some serious fragmentation issues < braunr> antrik: both could be induced by fragmentation + +--- + +During [[IPC_virtual_copy]] testing: + +IRC, freenode, #hurd, 2011-09-02: + + <manuel> interestingly, running it several times has made the performance + drop quite much (i'm getting 400-500MB/s with 1M now, compared to nearly + 800 fifteen minutes ago) + <braunr> manuel: i observed the same behaviour + [...] diff --git a/open_issues/performance/ipc_virtual_copy.mdwn b/open_issues/performance/ipc_virtual_copy.mdwn new file mode 100644 index 00000000..00fa7180 --- /dev/null +++ b/open_issues/performance/ipc_virtual_copy.mdwn @@ -0,0 +1,358 @@ +[[!meta copyright="Copyright © 2011 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]]."]]"""]] + +IRC, freenode, #hurd, 2011-09-02: + + <slpz> what's the usual throughput for I/O operations (like "dd + if=/dev/zero of=/dev/null") in one of those Xen based Hurd machines + (*bber)? + <braunr> good question + <braunr> slpz: but don't use /dev/zero and /dev/null, as they don't have + anything to do with true I/O operations + <slpz> braunr: in fact, I want to test the performance of IPC's virtual + copy operations + <braunr> ok + <slpz> braunr: sorry, the "I/O" was misleading + <braunr> use bs=4096 then i guess + <slpz> bs > 2k + <braunr> ? + <slpz> braunr: everything about 2k is copied by vm_map_copyin/copyout + <slpz> s/about/above/ + <slpz> braunr: MiG's stubs check for that value and generate complex (with + out_of_line memory) messages if datalen is above 2k, IIRC + <braunr> ok + <braunr> slpz: found it, thanks + <tschwinge> tschwinge@strauss:~ $ dd if=/dev/zero of=/dev/null bs=4k & p=$! + && sleep 10 && kill -s INFO $p && sleep 1 && kill $p + <tschwinge> [1] 13469 + <tschwinge> 17091+0 records in + <tschwinge> 17090+0 records out + <tschwinge> 70000640 bytes (70 MB) copied, 17.1436 s, 4.1 MB/s + <tschwinge> Note, however 10 s vs. 17 s! + <tschwinge> And this is slow compared to heal hardware: + <tschwinge> thomas@coulomb:~ $ dd if=/dev/zero of=/dev/null bs=4k & p=$! && + sleep 10 && kill -s INFO $p && sleep 1 && kill $p + <tschwinge> [1] 28290 + <tschwinge> 93611+0 records in + <tschwinge> 93610+0 records out + <tschwinge> 383426560 bytes (383 MB) copied, 9.99 s, 38.4 MB/s + <braunr> tschwinge: is the first result on xen vm ? + <tschwinge> I think so. + <braunr> :/ + <slpz> tschwinge: Thanks! Could you please try with a higher block size, + something like 128k or 256k? + <tschwinge> strauss is on a machine that also hosts a buildd, I think. + <braunr> oh ok + <pinotree> yes, aside either rossini or mozart + <tschwinge> And I can confirm that with dd if=/dev/zero of=/dev/null bs=4k + running, a parallel sleep 10 takes about 20 s (on strauss). + +[[open_issues/time]] + + <braunr> slpz: i'll set up xen hosts soon and can try those tests while + nothing else runs to have more accurate results + <tschwinge> tschwinge@strauss:~ $ dd if=/dev/zero of=/dev/null bs=256k & + p=$! && sleep 10 && kill -s INFO $p && sleep 1 && kill $p + <tschwinge> [1] 13482 + <tschwinge> 4566+0 records in + <tschwinge> 4565+0 records out + <tschwinge> 1196687360 bytes (1.2 GB) copied, 13.6751 s, 87.5 MB/s + <braunr> slpz: gains are logarithmic beyond the page size + <tschwinge> thomas@coulomb:~ $ dd if=/dev/zero of=/dev/null bs=256k & p=$! + && sleep 10 && kill -s INFO $p && sleep 1 && kill $p + <tschwinge> [1] 28295 + <tschwinge> 6335+0 records in + <tschwinge> 6334+0 records out + <tschwinge> 1660420096 bytes (1.7 GB) copied, 9.99 s, 166 MB/s + <tschwinge> This time a the sleep 10 decided to take 13.6 s. + ``Interesting.'' + <slpz> tschwinge: Thanks again. The results for the Xen machine are not bad + though. I can't obtain a throughput over 50MB/s with KVM. + <tschwinge> slpz: Want more data (bs)? Just tell. + <braunr> slpz: i easily get more than that + <braunr> slpz: what buffer size do you use ? + <slpz> tschwinge: no, I just wanted to see if Xen has an upper limit beyond + KVM's. Thank you. + <slpz> braunr: I try with different sizes until I find the maximum + throughput for a certain amount of requests (count) + <slpz> braunr: are you working with KVM? + <braunr> yes + <braunr> slpz: my processor is a model name : Intel(R) Core(TM)2 Duo + CPU E7500 @ 2.93GHz + <braunr> Linux silvermoon 2.6.32-5-amd64 #1 SMP Tue Jun 14 09:42:28 UTC + 2011 x86_64 GNU/Linux + <braunr> (standard amd64 squeeze kernel) + <slpz> braunr: and KVM's version? + <braunr> squeeze (0.12.5) + <braunr> bbl + <gnu_srs> 212467712 bytes (212 MB) copied, 9.95 s, 21.4 MB/s on kvm for me! + <slpz> gnu_srs: which block size? + <gnu_srs> 4k, and 61.7 MB/s with 256k + <slpz> gnu_srs: could you try with 512k and 1M? + <gnu_srs> 512k: 56.0 MB/s, 1024k: 40.2 MB/s Looks like the peak is around a + few 100k + <slpz> gnu_srs: thanks! + <slpz> I've just obtained 1.3GB/s with bs=512k on other (newer) machine + <braunr> on which hw/vm ? + <slpz> I knew this is a cpu-bound test, but I couldn't imagine faster + processors could make this difference + <slpz> braunr: Intel(R) Core(TM) i5 CPU 650 @ 3.20GHz + <slpz> braunr: KVM + <braunr> ok + <braunr> how much time did you wait before reading the result ? + <slpz> that was 20x times better than the same test on my Intel(R) + Core(TM)2 Duo CPU T7500 @ 2.20GHz + <slpz> braunr: I've repeated the test with a fixed "count" + <gnu_srs> My box is: Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz: Max + is 67 MB/s around 140k block size + <braunr> yes but how much time did dd run ? + <gnu_srs> 10 s plus/minus a few fractions of a second, + <braunr> try waiting 30s + <slpz> braunr: didn't check, let me try again + <braunr> my kvm peaks at 130 MiB/s with bs 512k / 1M + <gnu_srs> 2029690880 bytes (2.0 GB) copied, 30.02 s, 67.6 MB/s, bs=140k + <braunr> gnu_srs: i'm very surprised with slpz's result of 1.3 GiB/s + <slpz> braunr: over 60 s running, same performance + <braunr> nice + <braunr> i wonder what makes it so fast + <braunr> how much cache ? + <gnu_srs> Me too, I cannot get better values than around 67 MB/s + <braunr> gnu_srs: same questions + <slpz> braunr: 4096KB, same as my laptop + <braunr> slpz: l2 ? l3 ? + <gnu_srs> kvm: cache=writeback, CPU: 4096 KB + <braunr> gnu_srs: this has nothing to do with the qemu option, it's about + the cpu + <slpz> braunr: no idea, it's the first time I touch this machine. I going + to see if I find the model in processorfinder + <braunr> under my host linux system, i get a similar plot, that is, + performance drops beyond bs=1M + <gnu_srs> braunr: OK, bu I gave you the cache size too, same as slpz. + <braunr> i wonder what dd actually does + <braunr> read() and writes i guess + <slpz> braunr: read/write repeatedly, nothing fancy + <braunr> slpz: i don't think it's a good test for virtual copy + <braunr> io_read_request, vm_deallocate, io_write_request, right + <braunr> slpz: i really wonder what it is about i5 that improves speed so + much + <slpz> braunr: me too + <slpz> braunr: L2: 2x256KB, L3: 4MB + <slpz> and something calling "SmartCache" + <gnu_srs> slpz: where did you find these values? + <slpz> gnu_srs: ark.intel.com and wikipedia + <gnu_srs> aha, cpuinfo just gives cache size. + <slpz> that "SmartCache" thing seems to be just L2 cache sharing between + cores. Shouldn't make a different since we're using only one core, and I + don't see KVM hooping between them. + <manuel> with bs=256k: 7004487680 bytes (7.0 GB) copied, 10 s, 700 MB/s + <manuel> (qemu/kvm, 3 * Intel(R) Xeon(R) E5504 2GHz, cache size 4096 KB) + <slpz> manuel: did you try with 512k/1M? + <manuel> bs=512k: 7730626560 bytes (7.7 GB) copied, 10 s, 773 MB/s + <manuel> bs=1M: 7896825856 bytes (7.9 GB) copied, 10 s, 790 MB/s + <slpz> manuel: those are pretty good numbers too + <braunr> xeon processor + <gnu_srs> lshw gave me: L1 Cache 256KiB, L2 cache 4MiB + <slpz> sincerely, I've never seen Hurd running this fast. Just checked + "uname -a" to make sure I didn't take the wrong image :-) + <manuel> for bs=256k, 60s: 40582250496 bytes (41 GB) copied, 60 s, 676 MB/s + <braunr> slpz: i think you can assume processor differences alter raw + copies too much to get any valuable results about virtual copy operations + <braunr> you need a specialized test program + <manuel> and bs=512k, 60s, 753 MB/s + <slpz> braunr: I'm using the mach_perf suite from OSFMach to do the + "serious" testing. I just wanted a non-synthetic test to confirm the + readings. + +[[!taglink open_issue_gnumach]] -- have a look at *mach_perf*. + + <braunr> manuel: how much cache ? 2M ? + <braunr> slpz: ok + <braunr> manuel: hmno, more i guess + <manuel> braunr: /proc/cpuinfo says cache size : 4096 KB + <braunr> ok + <braunr> manuel: performance should drop beyond bs=2M + <braunr> but that's not relevant anyway + <gnu_srs> Linux: bs=1M, 10.8 GB/s + <slpz> I think this difference is too big to be only due to a bigger amount + of CPU cycles... + <braunr> slpz: clearly + <slpz> gnu_srs: your host system has 64 or 32 bits? + <slpz> braunr: I'm going to investigate a bit + <slpz> but this accidental discovery just made my day. We're able to run + Hurd at decent speeds on newer hardware! + <braunr> slpz: what result do you get with the same test on your host + system ? + <manuel> interestingly, running it several times has made the performance + drop quite much (i'm getting 400-500MB/s with 1M now, compared to nearly + 800 fifteen minutes ago) + +[[Degradataion]]. + + <slpz> braunr: probably an almost infinite throughput, but I don't consider + that a valid test, since in Linux, the write operation to "/dev/null" + doesn't involve memory copying/moving + <braunr> manuel: i observed the same behaviour + <gnu_srs> slpz: Host system is 64 bit + <braunr> slpz: it doesn't on the hurd either + <braunr> slpz: (under 2k, that is) + <braunr> over* + <slpz> braunr: humm, you're right, as the null translator doesn't "touch" + the memory, CoW rules apply + <braunr> slpz: the only thing which actually copies things around is dd + <braunr> probably by simply calling read() + <braunr> which gets its result from a VM copy operation, but copies the + content to the caller provided buffer + <braunr> then vm_deallocate() the data from the storeio (zero) translator + <braunr> if storeio isn't too dumb, it doesn't even touch the transfered + buffer (as anonymous vm_map()ped memory is already cleared) + +[[!taglink open_issue_documentation]] + + <braunr> so this is a good test for measuring (profiling?) our ipc overhead + <braunr> and possibly the vm mapping operations (which could partly explain + why the results get worse over time) + <braunr> manuel: can you run vminfo | wc -l on your gnumach process ? + <slpz> braunr: Yes, unless some special situation apply, like the source + address/offset being unaligned, or if the translator decides to return + the result in a different buffer (which I assume is not the case for + storeio/zero) + <manuel> braunr: 35 + <braunr> slpz: they can't be unaligned, the vm code asserts that + <braunr> manuel: ok, this is normal + <slpz> braunr: address/offset from read() + <braunr> slpz: the caller provided buffer you mean ? + <slpz> braunr: yes, and the offset of the memory_object, if it's a pager + based translator + <braunr> slpz: highly unlikely, the compiler chooses appropriate alignments + for such buffers + <slpz> braunr: in those cases, memcpy is used over vm_copy + <braunr> slpz: and the glibc memcpy() optimized versions can usually deal + with that + <braunr> slpz: i don't get your point about memory objects + <braunr> slpz: requests on memory objects always have aligned values too + <slpz> braunr: sure, but can't deal with the user requesting non + page-aligned sizes + <braunr> slpz: we're considering our dd tests, for which we made sure sizes + were page aligned + <slpz> braunr: oh, I was talking in a general sense, not just in this dd + tests, sorry + <slpz> by the way, dd on the host tops at 12 GB/s with bs=2M + <braunr> that's consistent with our other results + <braunr> slpz: you mean, even on your i5 processor with 1.3 GiB/s on your + hurd kvm ? + <slpz> braunr: yes, on the GNU/Linux which is running as host + <braunr> slpz: well that's not consistent + <slpz> braunr: consistent with what? + <braunr> slpz: i get roughly the same result on my host, but ten times less + on my hurd kvm + <braunr> slpz: what's your kernel/kvm versions ? + <slpz> 2.6.32-5-amd64 (debian's build) 0.12.5 + <braunr> same here + <braunr> i'm a bit clueless + <braunr> why do i only get 130 MiB/s where you get 1.3 .. ? :) + <slpz> well, on my laptop, where Hurd on KVM tops on 50 MB/s, Linux gets a + bit more than 10 GB/s + <braunr> see + <braunr> slpz: reduce bs to 256k and test again if you have time please + <slpz> braunr: on which system? + <braunr> slpz: the fast one + <braunr> (linux host) + <slpz> braunr: Hurd? + <slpz> ok + <slpz> 12 GB/s + <braunr> i get 13.3 + <slpz> same for 128k, only at 64k starts dropping + <slpz> maybe, on linux we're being limited by memory speed, while on Hurd's + this test is (much) more CPU-bound? + <braunr> slpz: maybe + <braunr> too bad processor stalls aren't easy to measure + <slpz> braunr: that's very true. It's funny when you read a paper which + measures performance by cycles on an old RISC processor. That's almost + impossible to do (with reliability) nowadays :-/ + <slpz> I wonder which throughput can achieve Hurd running bare-metal on + this machine... + <antrik> both the Xeon and the i5 use cores based on the Nehalem + architecture + <antrik> apparently Nehalem is where Intel first introduces nested page + tables + <antrik> which pretty much explains the considerably lower overhead of VM + magic + <cjuner> antrik, what are nested page tables? (sounds like the 4-level page + tables we already have on amd64, or 2-level or 3-level on x86 pae) + <antrik> page tables were always 2-level on x86 + <antrik> that's unrelated + <antrik> nested page tables means there is another layer of address + translation, so the VMM can do it's own translation and doesn't care what + the guest system does => no longer has to intercept all page table + manipulations + <braunr> antrik: do you imply it only applies to virtualized systems ? + <antrik> braunr: yes + <slpz> antrik: Good guess. Looks like Intel's EPT are doing the trick by + allowing the guest OS deal with its own page faults + <slpz> antrik: next monday, I'll try disabling EPT support in KVM on that + machine (the fast one). That should confirm your theory empirically. + <slpz> this also means that there're too many page faults, as we should be + doing virtual copies of memory that is not being accessed + <slpz> and looking at how the value of "page faults" in "vmstat" increases, + shows that page faults are directly proportional to the number of pages + we are asking from the translator + <slpz> I've also tried doing a long read() directly, to be sure that "dd" + is not doing something weird, and it shows the same behaviour. + <braunr> slpz: dd does copy buffers + <braunr> slpz: i told you, it's not a good test case for pure virtual copy + evaluation + <braunr> antrik: do you know if xen benefits from nested page tables ? + <antrik> no idea + +[[!taglink open_issue_xen]] + + <slpz> braunr: but my small program doesn't, and still provokes a lot of + page faults + <braunr> slpz: are you certain it doesn't ? + <slpz> braunr: looking at google, it looks like recent Xen > 3.4 supports + EPT + <braunr> ok + <braunr> i'm ordering my new server right now, core i5 :) + <slpz> braunr: at least not explicitily. I need to look at MiG stubs again, + I don't remember if they do something weird. + <antrik> braunr: sandybridge or nehalem? :-) + <braunr> antrik: no idea + <antrik> does it tell a model number? + <braunr> not yet + <braunr> but i don't have a choice for that, so i'll order it first, check + after + <antrik> hehe + <antrik> I'm not sure it makes all that much difference anyways for a + server... unless you are running it at 100% load ;-) + <braunr> antrik: i'm planning on running xen guests suchs as new buildd + <antrik> hm... note though that some of the nehalem-generation i5s were + dual-core, while all the new ones are quad + <braunr> it's a quad + <antrik> the newer generation has better performance per GHz and per + Watt... but considering that we are rather I/O-limited in most cases, it + probably won't make much difference + <antrik> not sure whether there are further virtualisation improvements + that could be relevant... + <braunr> buildds spend much time running gcc, so even such improvements + should help + <braunr> there, server ordered :) + <braunr> antrik: model name : Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz + +IRC, freenode, #hurd, 2011-09-06: + + <slpz> youpi: what machines are being used for buildd? Do you know if they + have EPT/RVI? + <youpi> we use PV Xen there + <slpz> I think Xen could also take advantage of those technologies. Not + sure if only in HVM or with PV too. + <youpi> only in HVM + <youpi> in PV it does not make sense: the guest already provides the + translated page table + <youpi> which is just faster than anything else diff --git a/open_issues/time.mdwn b/open_issues/time.mdwn index eda5b635..ab239aef 100644 --- a/open_issues/time.mdwn +++ b/open_issues/time.mdwn @@ -1,4 +1,4 @@ -[[!meta copyright="Copyright © 2009 Free Software Foundation, Inc."]] +[[!meta copyright="Copyright © 2009, 2011 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 @@ -53,3 +53,17 @@ GNU time's *elapsed* value is off by some factor. As above; also here all the running time should be attriuted to *user* time. This is probably a [[!taglink open_issue_gnumach]]. + + +# 2011-09-02 + +Might want to revisit this, and take Xen [[!tag open_issue_xen]] into account +-- I believe flubber has already been Xenified at that time. + + +## IRC, freenode, #hurd, 2011-09-02 + +While testing some [[performance/IPC_virtual_copy]] performance issues: + + <tschwinge> And I can confirm that with dd if=/dev/zero of=/dev/null bs=4k + running, a parallel sleep 10 takes about 20 s (on strauss). diff --git a/open_issues/translators_set_up_by_untrusted_users.mdwn b/open_issues/translators_set_up_by_untrusted_users.mdwn index cee7a2bc..36fe5438 100644 --- a/open_issues/translators_set_up_by_untrusted_users.mdwn +++ b/open_issues/translators_set_up_by_untrusted_users.mdwn @@ -281,3 +281,46 @@ Protection](https://wiki.ubuntu.com/SecurityTeam/Roadmap/KernelHardening#Symlink and [Hardlink Protection](https://wiki.ubuntu.com/SecurityTeam/Roadmap/KernelHardening#Hardlink_Protection) do bear some similarity with the issue we're discussing here. + + +# IRC, freenode, #hurd, 2011-08-31 + + <antrik> I don't see any problems with following only translators of + trusted users + <youpi> where to store the list of trusted users? + <youpi> is there a way to access the underlying node, which for /dev + entries belongs to root? + <ArneBab> youpi: why a list of trusted users? Does it not suffice to + require /hurd/trust set by root or ourselves? + <youpi> ArneBab: just because that's what antrik suggests, so I ask him for + more details + <ArneBab> ah, ok + <antrik> youpi: probably make them members of a group + <antrik> of course that doesn't allow normal users to add their own trusted + users... but that's not the only limitation of the user-based + authentication mechanism, so I wouldn't consider that an extra problem + <antrik> ArneBab: we can't set a translator on top of another user's + translator in general + <antrik> root could, but that's not very flexible... + <antrik> the group-based solution seems more useful to me + <ArneBab> antrik: why can’t we? + <antrik> also note that you can't set passive translators on top of other + translators + <antrik> ArneBab: because we can only set translators on our own nodes + <ArneBab> active ones, too? + <antrik> yes + <ArneBab> antrik: I always thought I could… + <ArneBab> but did not test it + <ArneBab> antrik: so I need a subhurd to change nodes which do not belong + to me? + * ArneBab in that case finally understands why you like subhurds so much: + That should be my normal right + <antrik> it should be your normal right to change stuff not belonging to + you? that's an odd world view :-) + <antrik> subhurds don't really have anything to do with it + <ArneBab> change it in a way that only I see the changes + <antrik> you need local namespaces to allow making local modifications to + global resources + <youpi> it should be one's normal right to change the view one has of it + <antrik> we discussed that once actually I believe... + <antrik> err... private namespaces I mean |