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

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Date:   Fri, 21 Jun 2019 10:11:58 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Andre Przywara <andre.przywara@....com>
Cc:     linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-kselftest@...r.kernel.org, Shuah Khan <shuah@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Huw Davies <huw@...eweavers.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Paul Burton <paul.burton@...s.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Collingbourne <pcc@...gle.com>
Subject: Re: [PATCH v6 00/19] Unify vDSOs across more architectures

On 20/06/2019 17:27, Andre Przywara wrote:
> On Thu, 30 May 2019 15:15:12 +0100
> Vincenzo Frascino <vincenzo.frascino@....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@....com>
>

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

> Cheers,
> Andre.
> 

-- 
Regards,
Vincenzo