linux-kernel - Re: [PATCH v3] x86/vdso: Handle clock_gettime(CLOCK

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Message-ID: <dde36e93-a21b-6223-8ffc-6dd11f687d38@redhat.com>
Date:   Wed, 12 Sep 2018 15:01:43 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Matt Rickard <matt@...trans.com.au>,
        Stephen Boyd <sboyd@...nel.org>,
        John Stultz <john.stultz@...aro.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] x86/vdso: Handle clock_gettime(CLOCK_TAI) in vDSO

On 09/09/2018 10:05 PM, Thomas Gleixner wrote:
> See the patch below. It's integrating TAI without slowing down everything
> and it definitely does not result in indirect calls.
> 
> On a HSW it slows down clock_gettime() by ~0.5ns. On a SKL I get a speedup
> by ~0.5ns. On a AMD Epyc server it's 1.2ns speedup. So it somehow depends
> on the uarch and I also observed compiler version dependend variations.

Does this mean glibc can keep using a single vDSO entrypoint, the one we 
have today?

Thanks,
Florian