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From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Cc: Jens Axboe <axboe@kernel.dk>,
	Daniel Vetter <daniel.vetter@ffwll.ch>,
	Eero Tamminen <eero.t.tamminen@intel.com>,
	"Rantala, Valtteri" <valtteri.rantala@intel.com>,
	stable@kernel.vger.org
Subject: Re: [PATCH v2 1/3] drm/i915: Break busywaiting for requests on pending signals
Date: Fri, 27 Nov 2015 16:51:55 +0000	[thread overview]
Message-ID: <56588A2B.1000500@linux.intel.com> (raw)
In-Reply-To: <1448634382-8987-1-git-send-email-chris@chris-wilson.co.uk>


On 27/11/15 14:26, Chris Wilson wrote:
> The busywait in __i915_spin_request() does not respect pending signals
> and so may consume the entire timeslice for the task instead of
> returning to userspace to handle the signal.
>
> In the worst case this could cause a delay in signal processing of 20ms,
> which would be a noticeable jitter in cursor tracking. If a higher
> resolution signal was being used, for example to provide fairness of a
> server timeslices between clients, we could expect to detect some
> unfairness between clients (i.e. some windows not updating as fast as
> others). This issue was noticed when inspecting a report of poor
> interactivity resulting from excessively high __i915_spin_request usage.
>
> Fixes regression from
> commit 2def4ad99befa25775dd2f714fdd4d92faec6e34 [v4.2]
> Author: Chris Wilson <chris@chris-wilson.co.uk>
> Date:   Tue Apr 7 16:20:41 2015 +0100
>
>       drm/i915: Optimistically spin for the request completion
>
> v2: Try to assess the impact of the bug

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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      parent reply	other threads:[~2015-11-27 16:51 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-11-27 14:26 [PATCH v2 1/3] drm/i915: Break busywaiting for requests on pending signals Chris Wilson
2015-11-27 14:26 ` [PATCH v2 2/3] drm/i915: Limit the busy wait on requests to 10us not 10ms! Chris Wilson
2015-11-27 16:52   ` Tvrtko Ursulin
2015-11-27 14:26 ` [PATCH v2 3/3] drm/i915: Only spin whilst waiting on the current request Chris Wilson
2015-11-27 16:51 ` Tvrtko Ursulin [this message]

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