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| -rw-r--r-- | open_issues/clock_gettime.mdwn | 345 | ||||
| -rw-r--r-- | open_issues/nanosecond-precision_clock.mdwn | 22 |
2 files changed, 22 insertions, 345 deletions
diff --git a/open_issues/clock_gettime.mdwn b/open_issues/clock_gettime.mdwn deleted file mode 100644 index 6f2ad6fd..00000000 --- a/open_issues/clock_gettime.mdwn +++ /dev/null @@ -1,345 +0,0 @@ -[[!meta copyright="Copyright © 2011, 2013, 2014 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]]."]]"""]] - -[[!meta title="clock_gettime"]] - -[[!tag open_issue_glibc open_issue_gnumach]] - -Missing `clock_gettime(CLOCK_MONOTONIC)` (e.g. for iceweasel) - -It could be a mere matter of extending the -[[mapped-time_interface|microkernel/mach/gnumach/interface/device/time]]: -add it to -`mapped_time_value_t` in gnumach, handle it in `gnumach/kern/mach_clock.c`, and -make `clock_gettime` use it. - -What about adding a nanosecond-precision clock, too? --[[tschwinge]] - - -# IRC, freenode, #hurd, 2011-08-26 - - < pinotree> youpi: thing is: apparently i found a simple way to have a - monotonic clock as mmap-able device inside gnumach - < pinotree> currently, in kern/mach_clock.c there's a variable 'time', - which gets increased on clock interrupt, and optionally modified by - host_set_time - < pinotree> () - < pinotree> if i add a new variable next to it, only increasing it on - interrupt but not modifying it at all otherwise, would that give me a - monotonic clock? - < pinotree> at least on sme basic tests i did, it seems it could work that - way - < 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. :-) - - -# IRC, freenode, #hurd, 2013-02-11 - -In context of [[select]]. - - <pinotree> braunr: would you send for review (and inclusion) your - time_data_t addition? - <pinotree> this way we could add nanosecs-based utime rpc (and then their - implementation in libc) - <braunr> pinotree: it's part of the hurd branch - <braunr> do you want it sent separately ? - <pinotree> yeah - <braunr> ok - <braunr> let me get it right first :) - <pinotree> sure :) - - -## IRC, freenode, #hurd, 2013-02-12 - - <braunr> pinotree: - https://git.savannah.gnu.org/cgit/hurd/hurd.git/commit/?h=rbraun/select_timeout_pthread_v2&id=6ec50e62d9792c803d00cbff1cab2c0b3675690a - <pinotree> uh nice - <pinotree> will need two small inline functions to convert time_data_t <-> - timespec, but that's it - <braunr> hm right - <braunr> i could have thought about it - <braunr> but i'll leave it for another patch :p - <pinotree> oh sure, no hurry - - -## IRC, freenode, #hurd, 2013-02-19 - - <youpi> braunr: about time_data_t, I get it's needed that it be an array - <youpi> so it can be passed by reference, not by value? - <braunr> by address, yes - <braunr> that's the difference between array and struct - - -## IRC, freenode, #hurd, 2013-02-25 - - <youpi> braunr: why did you want to see time_data passed as pointer, not as - struct? - <braunr> to microoptimize - <braunr> the struct is 2 64-bit integers - <youpi> well, we already pass structs along in a few cases, - e.g. io_statbuf_t, rusage_t, etc. - <youpi> be it written t[0].sec or t->sec, it seems odd - <youpi> copying 2 64bit integers is not much compared to the potential for - bugs here - <braunr> bugs ? - <youpi> yes, as in trying to access t[1], passing a wrong pointer, etc. - <youpi> or the reader frowning on "why is this case different than the - others?" - <braunr> well, i'm already usually frowning when i see what mig does .. - <youpi> right - <youpi> on the plus side, it's only the client side, i.e. mostly glibc, - which sees the t[0] - <braunr> and the practice established by my patch is to convert to struct - timespec as soon as possible - <braunr> the direct use of this type is therefore limited - <youpi> could we define time_data_t as a struct time_data * instead of - struct time_data[1] ? - <youpi> (in the.h) - <youpi> that would make more sense to define a struct time_data, and pass a - pointer to it - <braunr> i'm not sure - <braunr> the mach server writing guide was very clear about array implying - a C array too - <braunr> and i remember having compilation problems before doing that - <braunr> but i don't remember their nature exactly - <youpi> I'm not sure to understand what you said about converting to struct - timespec - <youpi> what makes it not possible now? - <youpi> and what is the relation with being an array or a pointer? - <braunr> concerning struct timespec, what i mean is that the functions - called by the mig stub code directly convert time_data_t to a struct - timespec (which is the real type used throughout the hurd code) - <braunr> about the rest, i'm not sure, i'd have to try again - <braunr> mig just assumes it's an array - <youpi> and why not just using struct timespec? - <youpi> (for the mig type too) - <braunr> my brain can't correctly compute variable sized types in mig - definition files - <braunr> i wanted something that would remain correct for the 64-bit port - -[[64-bit_port]], [[mig_portable_rpc_declarations]]. - - <youpi> ah, you mean because tv_nsec is a long, which will not be the same - type? - <braunr> and tv_sec being a time_t (thus a long too) - <youpi> but we have the same issue e.g. for the rusage structure, don't we? - <braunr> yes - <youpi> so we'll have to fix things for that too anyway - <braunr> sure - <youpi> making a special case will not necessarily help - <braunr> but it doesn't mean new interfaces have to be buggy too - <youpi> well, using the proper type in the server itself is nicer - <youpi> instead of having to convert - <braunr> yes - <braunr> i'm not exactly sure where to declare struct timespec then - <braunr> should it be declared in hurd_types.h, and simply reused by the - libc headers ? - <youpi> ? AIUI, it's the converse, hurd_types.h uses the struct timespec - from libc headers, and defines timespec_t - <braunr> ok - <youpi> timespec_t being the internal type whose definition gets done right - for mig to do the right thing - <braunr> yes - <braunr> i see - <braunr> so, you'd like a struct of integer_t instead of an array of - signed64 - <youpi> for our current 32bit userland yes - <braunr> do you want to make the changes yourself or should i add a new - branch ? - <youpi> and we'll make that a 64bit struct when we have a64bit userland - - -# IRC, freenode, #hurd, 2013-04-06 - - <tschwinge> pinotree: You had once been working on adding nsec-procision - timestamps to GNU Mach's maptime interface (or what the name is). Is - that blocked on something or just waiting to be continued? - <pinotree> blocked on me needing to learn more the proper way to do - "atomic" update of the struct with time :) - - -# IRC, freenode, #hurd, 2013-09-04 - - <teythoon> do we have CLOCK_MONOTONIC ? - <braunr> teythoon: i think we do but it's actually a simple offset from - CLOCK_REALTIME .. :) - <teythoon> ah never mind, I do hate this posix time interface anyways - <braunr> really ? - <braunr> i think librt is decent - - -# Candidate for [[vDSO]] code? - - -# IRC, freenode, #hurd, 2014-02-23 - - <desrt> GLib (gthread-posix.c): Unexpected error from C library during - 'pthread_condattr_setclock': Invalid argument. Aborting. - <desrt> uh oh... - <desrt> time to go digging in glibc i guess... - <braunr> what are you trying to run ? - <desrt> glib - <braunr> with what ? - <desrt> just running glib's test suite under jhbuild - <desrt> i maintain glib and i made some changes recently -- i wanted to - make sure they didn't break the hurd - <desrt> and it seems they have ;/ - <braunr> well - <braunr> the hurd doesn't completely comply with posix 2008 - <desrt> long story short: we've keyed our timed waits on condition - variables to the monotonic clock for a long time now, but we never tested - that it actually worked - <desrt> so i just added an assert -- and indeed it fails on hurd - <braunr> our glibc lies about supporting timers - <braunr> good thinking - <braunr> we don't support the monotonic clock - <desrt> clock_gettime(CLOCK_MONOTONIC) seems to work - <braunr> and you should know that, even if clock selection and timers are - available (which posix 2008 requires), it's still optional - <braunr> no, glibc lies - <desrt> !! - <braunr> our "support" is a mere hack shifting CLOCK_REALTIME - <desrt> it should at least lie consistently :) - <braunr> we need to implement CLOCK_MONOTONIC properly - <desrt> ya... that would be very nice indeed - <braunr> not that hard either - <desrt> i agree! - <braunr> we just have to do it right - <desrt> fwiw, i plan to keep this assert in glib - <braunr> yes, it's good - <desrt> is there anywhere i can file a bug to give you guys some advance - warning? - <braunr> i don't think it's needed - <braunr> we know the problem - <desrt> k -- consider yourself warned, then :) - <braunr> and it's been a bigger concern recently - <desrt> awesome. glad i don't have to do anything :) - <braunr> if it's not already done, i suggest you check for the - CLOCK_MONOTONIC option - <desrt> fwiw, i'm trying to get a regular debian/gnu/hurd build of - glib/gtk/etc setup - <braunr> regular ? - <desrt> ya... out of git master on a daily basis - <braunr> from sources ? - <braunr> oh nice - <desrt> we recently set this up for freebsd as well - <braunr> few maintainers take the pain :) - <desrt> our non-linux 'problem discovery' is a bit crap before now :/ - <braunr> i guess that's pretty normal - <braunr> i don't consider it the responsibility of the maintainers to test - every possible platform - <desrt> glib is a bit unique -- portability is our business - <braunr> taking our patches into consideration is what we ask most - <braunr> right - <desrt> and the "please take the patches" thing is something we want to - stop doing - <braunr> why ? - <desrt> mostly because we often look at a patch that someone sent a few - years ago and say "do we even still need this?" - <desrt> and have no way to know - <braunr> uh - <desrt> you would not believe how many patches like this we've - accumulated... - <braunr> but if we send it now ? :) - <desrt> braunr: new policy is roughly this: - https://wiki.gnome.org/Projects/GLib/SupportedPlatforms - <desrt> ie: fixes for issues that are general portability improvements and - POSIX compliance are welcome... - <desrt> patches that introduce platform-specific #ifdef sections are - rejected unless we have a regular builder to test that code - <braunr> i see - <braunr> again, regarding portability, don't consider CLOCK_MONOTONIC to be - readily available, check for it - <braunr> an #error would be enough but it has to be checked - <desrt> it basically comes down to: we don't want to have code in our - version control that we have no possible way of testing - <braunr> yes - <desrt> braunr: we do check for it - <braunr> ok - <desrt> we assert() if clock_gettime(CLOCK_MONOTONIC) fails - <braunr> no i mean - <desrt> as POSIX said it should if CLOCK_MONOTONIC is not supported - <desrt> if you lie to us.... well, not much we can do - <braunr> POSIX_MONOTONIC_CLOCK - <braunr> _POSIX_MONOTONIC_CLOCK - <desrt> this is actually defined to 0 on most platforms... - <desrt> which does not mean that it's unsupported -- it means that the - runtime must be ready to deal with it not actually existing at runtime - <braunr> really ? - <desrt> yes - <desrt> we used to rely on this and got a bug that we were doing it wrong - :) - <desrt> and indeed, even on linux, both with glibc and uclibc: - <desrt> /usr/include/bits/posix_opt.h:#define _POSIX_MONOTONIC_CLOCK - 0 - <desrt> /usr/include/uClibc/bits/posix_opt.h:#define _POSIX_MONOTONIC_CLOCK - 0 - <braunr> ok it's described in 2.1.6 Options - <braunr> so your check is appropriate - <desrt> so does clock_gettime(MONOTONIC) on debian/hurd get me realtime? - <braunr> either that, or a value shifted from it - <desrt> if so, i'll just hack out the condattr_setclock() check and proceed - trying to build past glib... - * desrt checks - <desrt> as it is, even the build of glib fails since we use some tools - linked against ourselves during the build process... - <desrt> 1393124084790000 1393124084790000 - <desrt> those look the same.... - <braunr> heh - <desrt> i also notice that your clocks are not very high precision :) - <braunr> that's right - <desrt> HZ = 100, i guess - <braunr> yes - <desrt> fair enough - <desrt> our mainloop doesn't support better-than-millisecond accuracy yet - anyway :) - <desrt> (although it will soon...) - <braunr> nice - - -## IRC, freenode, #hurd, 2014-03-05 - - <desrt> braunr: bit of a warning: i released the glib that depends on - working pthread_condattr_setclock(..._MONOTONIC) and pochu said that it - will be landing in debian within the next days - <braunr> desrt: ok diff --git a/open_issues/nanosecond-precision_clock.mdwn b/open_issues/nanosecond-precision_clock.mdwn new file mode 100644 index 00000000..65690e96 --- /dev/null +++ b/open_issues/nanosecond-precision_clock.mdwn @@ -0,0 +1,22 @@ +[[!meta copyright="Copyright © 2011, 2013, 2014, 2025 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]]."]]"""]] + +[[!meta title="a nanosecond-precision clock"]] + +[[!tag open_issue_glibc open_issue_gnumach]] + +What about adding a nanosecond-precision clock, too? --[[tschwinge]] + +The y2038 64b interfaces and the mapped time already support it, but the +granularity is still the clock tick period. + +# Candidate for [[vDSO]] code? + |