linux-kernel - Re: [patch v12 00/13] extensible prctl task isolation interface and vmstat sync

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Date:   Thu, 17 Mar 2022 16:08:04 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Nitesh Lal <nilal@...hat.com>,
        Nicolas Saenz Julienne <nsaenzju@...hat.com>,
        Christoph Lameter <cl@...ux.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Alex Belits <abelits@...its.com>, Peter Xu <peterx@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Oscar Shiang <oscar0225@...email.tw>
Subject: Re: [patch v12 00/13] extensible prctl task isolation interface and
 vmstat sync

On Tue, Mar 15, 2022 at 12:31:32PM -0300, Marcelo Tosatti wrote:
> The logic to disable vmstat worker thread, when entering
> nohz full, does not cover all scenarios. For example, it is possible
> for the following to happen:
> 
> 1) enter nohz_full, which calls refresh_cpu_vm_stats, syncing the stats.
> 2) app runs mlock, which increases counters for mlock'ed pages.
> 3) start -RT loop
> 
> Since refresh_cpu_vm_stats from nohz_full logic can happen _before_
> the mlock, vmstat shepherd can restart vmstat worker thread on
> the CPU in question.
> 
> To fix this, add task isolation prctl interface to quiesce
> deferred actions when returning to userspace.
> 
> The patchset is based on ideas and code from the
> task isolation patchset from Alex Belits:
> https://lwn.net/Articles/816298/
> 
> Please refer to Documentation/userspace-api/task_isolation.rst
> (patch 1) for details. Its attached at the end of this message
> in .txt format as well.
> 
> Note: the prctl interface is independent of nohz_full=.
> 
> The userspace patches can be found at https://people.redhat.com/~mtosatti/task-isol-v6-userspace-patches/
> 
> - qemu-task-isolation.patch: activate task isolation from CPU execution loop
> - rt-tests-task-isolation.patch: add task isolation activation to cyclictest/oslat
> - util-linux-chisol.patch: add chisol tool to util-linux.

I still see a few details to sort out but overall the whole thing looks good:

  Acked-by: Frederic Weisbecker <fweisbec@...il.com>

Perhaps it's time to apply this patchset on some branch and iterate from there.

Thomas, Peter, what do you think?

Thanks!