linux-kernel - Re: [RFC PATCH 6/6] cpuset: Add cpuset.isolation

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Message-ID: <20210719131704.GA116346@lothringen>
Date:   Mon, 19 Jul 2021 15:17:04 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        Nitesh Lal <nilal@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Saenz <nsaenzju@...hat.com>,
        Christoph Lameter <cl@...two.de>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH 6/6] cpuset: Add cpuset.isolation_mask file

On Thu, Jul 15, 2021 at 11:04:19AM +0200, Peter Zijlstra wrote:
> On Thu, Jul 15, 2021 at 01:13:38AM +0200, Frederic Weisbecker wrote:
> > On Wed, Jul 14, 2021 at 06:52:43PM +0200, Peter Zijlstra wrote:
> 
> > > cpusets already has means to create paritions; why are you creating
> > > something else?
> > 
> > I was about to answer that the semantics of isolcpus, which reference
> > a NULL domain, are different from SD_LOAD_BALANCE implied by
> > cpuset.sched_load_balance. But then I realize that SD_LOAD_BALANCE has
> > been removed.
> > 
> > How cpuset.sched_load_balance is implemented then? Commit
> > e669ac8ab952df2f07dee1e1efbf40647d6de332 ("sched: Remove checks against
> > SD_LOAD_BALANCE") advertize that setting cpuset.sched_load_balance to 0
> > ends up creating NULL domain but that's not what I get. For example if I
> > mount a single cpuset root (no other cpuset mountpoints):
> 
> SD_LOAD_BALANCE was only for when you wanted to stop balancing inside a
> domain tree. That no longer happens (and hasn't for a *long* time).
> Cpusets simply creates multiple domain trees (or the empty one if its
> just one CPU).

Ok.

> 
> > $ mount -t cgroup none ./cpuset -o cpuset
> > $ cd cpuset
> > $ cat cpuset.cpus
> > 0-7
> > $ cat cpuset.sched_load_balance
> > 1
> > $ echo 0 > cpuset.sched_load_balance
> > $ ls /sys/kernel/debug/domains/cpu1/
> > domain0  domain1
> > 
> > I still get the domains on all CPUs...
> 
> (note, that's the cgroup-v1 interface, the cgroup-v2 interface is
> significantly different)
> 
> I'd suggest doing: echo 1 > /debug/sched/verbose, if I do the above I
> get:
> 
> [1290784.889705] CPU0 attaching NULL sched-domain.
> [1290784.894830] CPU1 attaching NULL sched-domain.

Thanks!

Eventually I uninstalled cgmanager and things seem to work now. I have
no idea why and I'm not sure I'm willing to investigate further :o)