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Date: Thu, 1 Mar 2018 17:09:20 +0100
From: Frederic Weisbecker <frederic@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>, mingo@kernel.org,
        linux-kernel@vger.kernel.org, valentin.schneider@arm.com,
        morten.rasmussen@foss.arm.com, brendan.jackman@arm.com,
        dietmar.eggemann@arm.com, Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [PATCH v3 3/3] sched: update blocked load when newly idle
Message-ID: <20180301160918.GC29639@lerouge>
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On Mon, Feb 12, 2018 at 04:38:05PM +0100, Peter Zijlstra wrote:
> On Mon, Feb 12, 2018 at 03:34:44PM +0100, Vincent Guittot wrote:
> > > Aside from the above being an unreadable mess, I dislike that it breaks
> > > the various isolation crud, we should not touch CPUs outside of our
> > > domain.
> > >
> > > 
> > > Maybe something like the below? (unfinished)
> > >
> > 
> > good catch. I completely miss the isolation stuff.
> > But isn't already the case when kicking ilb ? I mean that an idle CPU touches
> > all idle CPUs and some can be outside its domain during ilb.
> 
> > Shouldn't we test housekeeping_cpu(cpu, HK_FLAG_SCHED) instead if we want to
> > make sure that an isolated/full nohz CPU will not be used for updating blocked
> > load of CPUs outside its domain ?
> 
> I _thought_ we had some 'housekeeping' crud in the ilb selection logic,
> but now I can't find it. Frederic?

I think you're referring to nohz_balance_idle(). The call is still there but HK_FLAG_SCHED
is unused for now. I initially turned it on by default on nohz_full but some people
complained. I don't recall why exactly. Anyway I'm waiting for a suitable interface
to use it.