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Re: [PATCH 1/1 Web] Open issues: Update clock_gettime page
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From: |
Samuel Thibault |
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Subject: |
Re: [PATCH 1/1 Web] Open issues: Update clock_gettime page |
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Date: |
Wed, 15 Jan 2025 01:03:27 +0100 |
Tuned and applied, thanks!
Zhaoming Luo, le mar. 14 janv. 2025 09:50:01 +0800, a ecrit:
> The clock_gettime(CLOCK_MONOTONIC) is implemented. See
>
> https://sourceware.org/git?p=glibc.git;a=commit;h=3782ffaf3e6c2a071df029b96712e596b5229838
>
> so this page is out of date.
>
> Rename the page to nanosecond-precision_clock, and remove the
> information about clock_gettime(CLOCK_MONOTONIC).
> ---
> open_issues/clock_gettime.mdwn | 345 --------------------
> open_issues/nanosecond-precision_clock.mdwn | 56 ++++
> 2 files changed, 56 insertions(+), 345 deletions(-)
> delete mode 100644 open_issues/clock_gettime.mdwn
> create mode 100644 open_issues/nanosecond-precision_clock.mdwn
>
> 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..e71e1558
> --- /dev/null
> +++ b/open_issues/nanosecond-precision_clock.mdwn
> @@ -0,0 +1,56 @@
> +[[!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]]
> +
> +# 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, 2013-04-06
> +
> + <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 :)
> +
> +# Candidate for [[vDSO]] code?
> --
> 2.47.1
>
>
--
Samuel
Battery 1: charging, 90%, charging at zero rate - will never fully charge.
-+- acpi - et pourtant, ca monte -+-