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

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Message-ID: <01ab4388-f259-e801-8c8a-f39b5abcfb52@nokia.com>
Date:   Thu, 27 Jun 2019 12:00:48 +0000
From:   "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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

Hello Thomas!

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:

Number of clock_gettime() calls in 10 seconds:

		Before		After		Diff
MONOTONIC	152404300	200825950	+32%
MONOTONIC_RAW	38804788	198765053	+412%
REALTIME	151672619	201371468	+33%


-- 
Best regards,
Alexander Sverdlin.