linux-kernel - Re: 9908859acaa9 cpuidle/menu: add per CPU PM QoS resume latency consideration

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Message-ID: <20170222143910.GV6515@twins.programming.kicks-ass.net>
Date:   Wed, 22 Feb 2017 15:39:10 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alex Shi <alex.shi@...aro.org>
Cc:     Mike Galbraith <efault@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rik van Riel <riel@...hat.com>
Subject: Re: 9908859acaa9 cpuidle/menu: add per CPU PM QoS resume latency
 consideration

On Wed, Feb 22, 2017 at 10:31:26PM +0800, Alex Shi wrote:
> 
> 
> On 02/22/2017 09:19 PM, Mike Galbraith wrote:
> > On Wed, 2017-02-22 at 14:12 +0100, Peter Zijlstra wrote:
> >> On Wed, Feb 22, 2017 at 01:56:37PM +0100, Mike Galbraith wrote:
> >>> Hi,
> >>>
> >>> Do we really need a spinlock for that in the idle loop?
> >>
> >> Urgh, that's broken on RT, you cannot schedule the idle loop.
> > 
> > That's what made me notice the obnoxious little bugger.
> 
> Hi Mike,
> 
> Sorry for this bug. Guess the rt_spin_lock call some function in
> rtmutex.c:995. Could you like to show me how to reproduce this bug?

Its not hard; spinlock_t ends up being a mutex, and this is ran from the
idle thread. What thread do you think we ought to run when we block
idle?