linux-kernel - Re: RFC on fixing mutex spinning on owner

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Message-ID: <CAD=GYpZVGwfk8Y8WTQpdgdm5qgxjsi_gVrnOswuWitEbhaWPbw@mail.gmail.com>
Date:	Wed, 16 Mar 2016 16:38:56 -0700
From:	Joel Fernandes <agnel.joel@...il.com>
To:	Greg Kroah-Hartman <greg@...ah.com>
Cc:	linux-rt-users@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	kernelnewbies <kernelnewbies@...linux.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: RFC on fixing mutex spinning on owner

Hi Greg,

On Wed, Mar 16, 2016 at 4:35 PM, Greg Kroah-Hartman <greg@...ah.com> wrote:
> On Wed, Mar 16, 2016 at 04:22:17PM -0700, Joel Fernandes wrote:
>> Hi,
>>
>> On a fairly recent kernel and android userspace, I am seeing that with
>> i915 driver is in a spin loop waiting for mutex owner to release it
>> (mutex_spin_on_owner).
>
> Why not provide a backtrace to the drm and i915 developers so that they
> can work on this?  The mailing lists you sent this to can't do much
> about this, sorry...

I am not sure if the problem is with the i915 driver, because the
mutex spin on owner stuff is mutex related so the mutex design may
potentially need a tweak (I mentioned a proposal of adding mutex
spinning time outs).
Also since this is latency issue related (I mentioned preemptoff
tracer and preempt disabled), I sent it to linux-rt-users. Thanks for
the tip about sending it to i915 developers, incase no one here has a
say in the matter, I can drop them a note later as well.

Thanks,

Joel