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Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime()

From Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Newsgroups linux.kernel
Subject Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime()
Date 2015-10-28 21:20 +0100
Message-ID <qoFmq-7nd-9@gated-at.bofh.it> (permalink)
References (10 earlier) <qoDND-6j4-5@gated-at.bofh.it> <qoE70-6pV-25@gated-at.bofh.it> <qoEql-6NV-15@gated-at.bofh.it> <qoEA2-6Ra-5@gated-at.bofh.it> <qoF34-71h-13@gated-at.bofh.it>
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On 10/28/2015 12:55 PM, Alex Smith wrote:
> On 28 October 2015 at 19:28, Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> wrote:
>> . 
> Clocksources are not per-CPU. If the CP0 counter is the current
> clocksource, then both the kernel and VDSO implementations of
> gettimeofday will read out the CP0 counter from whatever CPU they run
> on.

OK, it was an invalid example. Let's be specific - in case of different 
clock frequency in different CPUs it easy to adjust it in kernel via 
clocksource->read()/etc but it is impossible to adjust that in VDSO 
implementation.

And that can't be fixed easily without some-kind of "per-thread" data 
page for correct multipliers.

There are many problems with assumption that in all kind of MIPS cores 
R4K CP0_COUNT registers are in sync in different CPUs. Even current 
kernel has problems here but I think it is not excuse to mount more on it.

- Leonid.


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[PATCH v3 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() Markos Chandras <markos.chandras@imgtec.com> - 2015-10-21 11:00 +0200
  Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-23 03:50 +0200
    Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Ralf Baechle <ralf@linux-mips.org> - 2015-10-27 15:50 +0100
      Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-27 21:50 +0100
        Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() David Daney <ddaney.cavm@gmail.com> - 2015-10-27 22:10 +0100
          Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-27 22:20 +0100
            Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-27 22:50 +0100
              Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() Alex Smith <alex@alex-smith.me.uk> - 2015-10-28 11:30 +0100
                Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-28 19:30 +0100
                Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() Alex Smith <alex@alex-smith.me.uk> - 2015-10-28 19:40 +0100
                Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-28 20:00 +0100
                Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() Alex Smith <alex@alex-smith.me.uk> - 2015-10-28 20:20 +0100
                Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-28 20:30 +0100
                Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime() Alex Smith <alex@alex-smith.me.uk> - 2015-10-28 21:00 +0100
                Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() Leonid Yegoshin <Leonid.Yegoshin@imgtec.com> - 2015-10-28 21:20 +0100
            Re: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and  clock_gettime() David Daney <ddaney.cavm@gmail.com> - 2015-10-27 22:50 +0100

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