Re: [PATCH v6 00/19] Unify vDSOs across more architectures

Vincenzo Frascino
2019-06-21T09:12:05Z

On 20/06/2019 17:27, Andre Przywara wrote:
> On Thu, 30 May 2019 15:15:12 +0100
> Vincenzo Frascino <vincenzo.frascino@arm.com> wrote:
>
> Hi,
>
>> vDSO (virtual dynamic shared object) is a mechanism that the Linux
>> kernel provides as an alternative to system calls to reduce where
>> possible the costs in terms of cycles.
>> [ ... ]
>> The porting has been benchmarked and the performance results are
>> provided as part of this cover letter.
>
> I can't reveal the absolute numbers here, but vdsotest-bench gives me
> quite some performance gain on my board here ("time needed on v6" divided
> by "time needed on 5.2-rc1", so smaller percentages are better):
> clock-gettime-monotonic: 23 %
> clock-gettime-monotonic-raw: 30 %
> clock-gettime-tai: 5 %
> clock-getres-tai: 5 %
> clock-gettime-boottime: 5 %
> clock-getres-boottime: 5 %
> clock-gettime-realtime: 25 %
> gettimeofday: 26 %
> The other numbers stayed the same or differed by just 1 ns, which seems to
> be within the margin of error, as repeated runs on the same kernel suggest.
> The 5% numbers are of course those were we went from a syscall-only to the
> newly added arm64 VDSO implementation, but even the other calls improved
> by a factor of 3 or more.
>
> Sounds like a strong indicator that this is a good thing to have.
>
> Not sure if "running some benchmark a couple of times on a single machine"
> qualifies for this, but I guess it means:
>
> Tested-by: Andre Przywara <andre.przywara@arm.com>
>

Thanks Andre, it sounds great! I will add your tag as well to my patches.

> Cheers,
> Andre.
>

--
Regards,
Vincenzo