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Date:   Mon, 25 Apr 2022 13:29:04 -0300
From:   Marcelo Tosatti <mtosatti@redhat.com>
To:     Frederic Weisbecker <frederic@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, Nitesh Lal <nilal@redhat.com>,
        Nicolas Saenz Julienne <nsaenzju@redhat.com>,
        Christoph Lameter <cl@linux.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Alex Belits <abelits@belits.com>, Peter Xu <peterx@redhat.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Oscar Shiang <oscar0225@livemail.tw>
Subject: Re: [patch v12 00/13] extensible prctl task isolation interface and
 vmstat sync
Message-ID: <YmbMUAkOxsStAP36@fuller.cnet>
References: <20220315153132.717153751@fedora.localdomain>
 <20220317150804.GB459366@lothringen>
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On Thu, Mar 17, 2022 at 04:08:04PM +0100, Frederic Weisbecker wrote:
> 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@gmail.com>
> 
> Perhaps it's time to apply this patchset on some branch and iterate from there.
> 
> Thomas, Peter, what do you think?
> 
> Thanks!

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