linux-kernel - Re: [RFD/RFC PATCH 5/8] sched: Add proxy execution

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Date:   Thu, 11 Oct 2018 15:42:24 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     luca abeni <luca.abeni@...tannapisa.it>, mingo@...hat.com,
        rostedt@...dmis.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, claudio@...dence.eu.com,
        tommaso.cucinotta@...tannapisa.it, alessio.balsini@...il.com,
        bristot@...hat.com, will.deacon@....com,
        andrea.parri@...rulasolutions.com, dietmar.eggemann@....com,
        patrick.bellasi@....com, henrik@...tad.us,
        linux-rt-users@...r.kernel.org
Subject: Re: [RFD/RFC PATCH 5/8] sched: Add proxy execution

On 11/10/18 14:53, Peter Zijlstra wrote:

[...]

> I think it was the safe and simple choice; note that we're not migrating
> just a single @p, but a whole chain of @p. rq->curr must not be any of the
> possible @p's. rq->idle, is per definition not one of the @p's.
> 
> Does that make sense?

It does, and I guess is most probably the safest choice indeed. But,
just to put together a proper comment for next version..

The chain we are migrating is composed of blocked_task(s), so tasks that
blocked on a mutex owned by @p. Now, if such a chain has been built, it
means that proxy() has been called "for" @p previously, and @p might be
curr while one of its waiters might be proxy. So, none of the blocked_
task(s) should be rq->curr (even if one of their scheduling context
might be in use)?