gpu: Ensure that preempted channels wake up after preemption.

gpu: Ensure that preempted channels wake up after preemption.

When a message queue is paused it is either due to preemption or being
descheduled. If it's because of preemption the message queue should post
a task to wake up later. Otherwise it will remain stuck forever and
because of sync token dependencies it's possible that the browser also
gets stuck.

BUG=591192
TEST=manual testing of hw accelerated video and webgl

Committed: https://crrev.com/f00f494dfc11b277c0b882735d9e1649d5156bea
Cr-Commit-Position: refs/heads/master@{#379895}

[sunnyps, 2016-03-08 02:51:46]

sunnyps@chromium.org changed reviewers:
+ piman@chromium.org

[sunnyps, 2016-03-08 02:51:46]

PTAL

[piman, 2016-03-08 16:22:41]

LGTM. Thanks for debugging this.
Not blocking this change, but do you think there's a way to test this, or is
that going to be easier to do with the scheduler?

[sunnyps, 2016-03-08 18:27:40]

The CQ bit was checked by sunnyps@chromium.org

[commit-bot: I haz the power, 2016-03-08 18:28:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1775763002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1775763002/1

[sunnyps, 2016-03-08 18:29:46]

Thanks for the review.

I think we can test the preemption state machine rather easily but that's not
where the bug was and is unlikely to be as well. I need to think about testing
message handling but I think we can test that too.

[commit-bot: I haz the power, 2016-03-08 20:07:46]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-03-08 20:08:46]

Description was changed from

==========
gpu: Ensure that preempted channels wake up after preemption.

When a message queue is paused it is either due to preemption or being
descheduled. If it's because of preemption the message queue should post
a task to wake up later. Otherwise it will remain stuck forever and
because of sync token dependencies it's possible that the browser also
gets stuck.

BUG=591192
TEST=manual testing of hw accelerated video and webgl
==========

to

==========
gpu: Ensure that preempted channels wake up after preemption.

When a message queue is paused it is either due to preemption or being
descheduled. If it's because of preemption the message queue should post
a task to wake up later. Otherwise it will remain stuck forever and
because of sync token dependencies it's possible that the browser also
gets stuck.

BUG=591192
TEST=manual testing of hw accelerated video and webgl

Committed: https://crrev.com/f00f494dfc11b277c0b882735d9e1649d5156bea
Cr-Commit-Position: refs/heads/master@{#379895}
==========

[commit-bot: I haz the power, 2016-03-08 20:08:47]

Patchset 1 (id:??) landed as
https://crrev.com/f00f494dfc11b277c0b882735d9e1649d5156bea
Cr-Commit-Position: refs/heads/master@{#379895}