linux-kernel - Re: [PATCH] mutex: Report recursive ww

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Message-ID: <1f1bcf7a-e1bc-e105-bcc6-8ca697fa9c4e@linux.intel.com>
Date:	Mon, 30 May 2016 13:16:28 +0200
From:	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	intel-gfx@...ts.freedesktop.org,
	Christian König <christian.koenig@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mutex: Report recursive ww_mutex locking early

Op 30-05-16 om 12:45 schreef Chris Wilson:
> On Mon, May 30, 2016 at 12:27:46PM +0200, Peter Zijlstra wrote:
>> On Mon, May 30, 2016 at 11:43:31AM +0200, Maarten Lankhorst wrote:
>>> Patch not applied, SCHED_RR:
>> ww_mutex isn't RT aware at all; its one of the things I still have on a
>> todo list. Should I look harder at finding time for this?
> The RT usage in the test is to just try and starve the kernel threads
> that may be used behind the atomic modeset - a problem we have
> encountered in the past. Afaik, no one is using ww_mutex from RT in the
> wild, calling the atomic modeset from the RT was just a shortcut to
> having the system fully populated with RT threads. To be more realistic
> we should be using a couple of normal modesetting threads vs a set of RT
> cpu hogs.
Yeah, unfortunately this doesn't work as you intend it to. You'd need to spawn a few more threads at slightly lower priority so when a thread is blocked waiting for acquisition of the mutexes the workqueues still can't run.

ssh is still responsive with the rest running.
> Otoh, i915.ko always draws the ire of rt-linux so ww_mutex is likely to
> be in their sights in the near future (when i915.ko completes its
> transition to full atomic modesetting).