linux-kernel - Re: [PATCH v3 1/2] x86/vdso: Move mult and shift into struct vgtod

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Date:   Thu, 27 Jun 2019 14:07:40 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
cc:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jason Vas Dias <jason.vas.dias@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>
Subject: Re: [PATCH v3 1/2] x86/vdso: Move mult and shift into struct
 vgtod_ts

Alexander,

On Thu, 27 Jun 2019, Sverdlin, Alexander (Nokia - DE/Ulm) wrote:

> On 24/06/2019 11:40, Thomas Gleixner wrote:
> >>> The alternative solution for this is what Vincenzo has in his unified VDSO
> >>> patch series:
> >>>
> >>>   https://lkml.kernel.org/r/20190621095252.32307-1-vincenzo.frascino@arm.com
> >>>
> >>> It leaves the data struct unmodified and has a separate array for the raw
> >>> clock. That does not have the side effects at all.
> >>>
> >>> I'm in the process of merging that series and I actually adapted your
> >>> scheme to the new unified infrastructure where it has exactly the same
> >>> effects as with your original patches against the x86 version.
> >> please let me know if I need to rework [2/2] based on some not-yet-published
> >> branch of yours.
> > I've pushed it out now to
> > 
> >      git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/vdso
> > 
> > The generic VDSO library has the support for RAW already with that separate
> > array. Testing would be welcomed!
> 
> Thanks for your and Vincenzo's efforts!
> I've applied the series onto 5.2.0-rc6 and did a quick test on a bare x86_64 and
> for me it looks good:

Did you use the git tree? If not, it would be interesting to have a test
against that as well because that's the final version.

> Number of clock_gettime() calls in 10 seconds:
> 
> 		Before		After		Diff
> MONOTONIC	152404300	200825950	+32%
> MONOTONIC_RAW	38804788	198765053	+412%
> REALTIME	151672619	201371468	+33%

The increase for mono and realtime is impressive. Which CPU is that?

Thanks,

	tglx