Date: Tue, 24 Nov 2015 09:12:40 +0000
From: Javi Merino <javi.merino@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Len Brown <len.brown@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Eduardo Valentin <edubezval@gmail.com>, Paul Turner <pjt@google.com>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>,
        Juri Lelli <Juri.Lelli@arm.com>
Subject: Re: [PATCH 3/4] sched: introduce synchronized idle injection
Message-ID: <20151124091239.GA2710@e104805>
References: <1447444387-23525-1-git-send-email-jacob.jun.pan@linux.intel.com>
 <1447444387-23525-4-git-send-email-jacob.jun.pan@linux.intel.com>
 <20151123175643.GA10703@e104805>
 <20151123180706.GN17308@twins.programming.kicks-ass.net>
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On Mon, Nov 23, 2015 at 07:07:06PM +0100, Peter Zijlstra wrote:
> On Mon, Nov 23, 2015 at 05:56:44PM +0000, Javi Merino wrote:
> > I've tested this series on Juno (2xCortex-A57 4xCortex-A53).  If you
> > idle inject for 50% of the time, when I run 6 busy loops the scheduler
> > sometimes keeps two of them in the same cpu while the another cpu is
> > completely idle.  Without idle injection the scheduler does the
> > sensible thing: put one busy loop in each CPU.  I'm running systemd
> > and this only happens with CONFIG_SCHED_AUTOGROUP=y.  If I unset
> > CONFIG_SCHED_AUTOGROUP, the tasks are spread across all cpus as usual.
> 
> That's not a plus for this patch though; but a bug report against
> AUTOGROUP/cgroup muck, right?

The bug only happens when you apply this series and you set the system
to idle inject 50% of the time.  SCHED_AUTOGROUP is already part of
the kernel and behaves properly with the kernel as is.  I think that
this patch should not introduce new bugs.

Cheers,
Javi
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