Re: RFC on fixing mutex spinning on owner

From: Joel Fernandes
Date: Wed Mar 16 2016 - 19:39:03 EST

Hi Greg,

On Wed, Mar 16, 2016 at 4:35 PM, Greg Kroah-Hartman <greg@xxxxxxxxx> 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.