linux-kernel - Re: [RFC PATCH v0.1 0/9] UMCG early preview/RFC patchset

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Date:   Fri, 21 May 2021 12:13:55 -0700
From:   Peter Oskolkov <posk@...gle.com>
To:     Andrei Vagin <avagin@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Peter Oskolkov <posk@...k.io>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jim Newsome <jnewsome@...project.org>
Subject: Re: [RFC PATCH v0.1 0/9] UMCG early preview/RFC patchset

On Fri, May 21, 2021 at 11:44 AM Andrei Vagin <avagin@...gle.com> wrote:
>
>
>
> On Thu, May 20, 2021 at 11:36 AM Peter Oskolkov <posk@...gle.com> wrote:
>>
>> As indicated earlier in the FUTEX_SWAP patchset:
>>
>> https://lore.kernel.org/lkml/20200722234538.166697-1-posk@posk.io/
>
>
> Hi Peter,
>
> Do you have benchmark results? How fast is it compared with futex_swap and the google switchto?

Hi Andrei,

I did not run benchmarks on the same machine/kernel, but umcg_swap
between "core" tasks (your use case for gVisor) should be somewhat
faster than futex_swap, as there is no reading from the userspace and
no futex hash lookup/dequeue ops; umcg_swap should be slower than
switchto_switch because umcg_swap does go through ttwu+schedule, which
switchto_switch bypasses.

I expect that if UMCG is merged in a form similar to what I posted, we
will explore how to make UMCG context switches faster in later
patches.

Thanks,
Peter

>
> Thanks,
> Andrei