[PATCH v7 0/9] ARM: VDSO

[Ard Biesheuvel]

On 1 July 2014 18:34, Nathan Lynch <Nathan_Lynch at mentor.com> wrote:
> On 06/30/2014 03:12 AM, Ard Biesheuvel wrote:
>> On 23 June 2014 05:11, Nathan Lynch <nathan_lynch at mentor.com> wrote:
>>> Provide fast userspace implementations of gettimeofday and
>>> clock_gettime on systems that implement the generic timers extension
>>> defined in ARMv7.
>
> ...
>
>> Tested-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>>
>> On Exynos-5250 (Cortex-A15):
>>
>> clock-gettime-monotonic system calls per second: 1759517
>> clock-gettime-monotonic vdso calls per second:   6027915 (3.43x speedup)
>> clock-getres-monotonic system calls per second: 2144055
>> clock-getres-monotonic vdso calls per second:   82783103 (38.61x speedup)
>> clock-gettime-monotonic-coarse system calls per second: 1971433
>> clock-gettime-monotonic-coarse vdso calls per second:   10710734 (5.43x speedup)
>> clock-getres-monotonic-coarse system calls per second: 2182380
>> clock-getres-monotonic-coarse vdso calls per second:   76710594 (35.15x speedup)
>> clock-gettime-realtime system calls per second: 1722524
>> clock-gettime-realtime vdso calls per second:   6309212 (3.66x speedup)
>> clock-getres-realtime system calls per second: 2182357
>> clock-getres-realtime vdso calls per second:   83120713 (38.09x speedup)
>> clock-gettime-realtime-coarse system calls per second: 2085498
>> clock-gettime-realtime-coarse vdso calls per second:   11326069 (5.43x speedup)
>> clock-getres-realtime-coarse system calls per second: 2178266
>> clock-getres-realtime-coarse vdso calls per second:   76731175 (35.23x speedup)
>> Note: vDSO version of getcpu not found
>> getcpu system calls per second: 2645300
>> getcpu vdso calls per second:   2612154 (0.99x speedup)
>> Note: vDSO version of getcpu not found
>> Note: vDSO version of getcpu not found
>> gettimeofday system calls per second: 1707745
>> gettimeofday vdso calls per second:   6474501 (3.79x speedup)
>
> Thank you very much for testing (especially on a platform I don't have).
>
> These results match up with what I get on OMAP5 (also Cortex-A15).
>

Good.

> Since it looks like I will need to make some significant changes for the
> next version, I think I can't in good conscience carry your Tested-by on
> to v8 (although I'm open to different opinions).  But I still very much
> appreciate it.
>

We (at Linaro) had independently identified VDSO for ARM as a topic of
interest after seeing gettimeofday() turn up in a couple of benchmarks
(which btw seem to be the primary users of gettimeofday() at such a
high rate), so of course, when someone else steps up and does the
work, i am happy to at least spend some time testing it. Therefore, I
would be happy to test your new version either before or after you
(re)post it, whichever you prefer.

Regards,
Ard.