Limit number of raster threads on Android.

Limit number of raster threads on Android.

The current formula for number of raster threads is (num_cpus / 2), minus
1 if using asynchronous uploads.

This will give:
 1~2 threads on 4 core devices
 2~3 threads on 6 core devices
 3~4 threads on 8 core devices

Android can report 6 to 8 cores for big.LITTLE devices, where we don't
really want to utilize all the cores at once.  This change limits the
cores to 4 in the render threads calculation.

R=sievers@chromium.org
R=reveman@chromium.org
BUG=493432
Committed: https://crrev.com/6bfd5d8926aa101b39b0d3548b5dfd6cfad8b734
Cr-Commit-Position: refs/heads/master@{#333599}

[vmiura, 2015-06-09 02:00:14]

Patchset #1 (id:1) has been deleted

[vmiura, 2015-06-09 02:00:55]

ptal

[reveman, 2015-06-09 02:17:07]

lgtm but maybe we should also update base::SysInfo to better accommodate these
devices. e.g. add a new function that is more suitable for multi-threading
decisions

[no sievers, 2015-06-09 18:26:31]

lgtm

https://codereview.chromium.org/1168153004/diff/20001/content/browser/gpu/com...
File content/browser/gpu/compositor_util.cc (right):

https://codereview.chromium.org/1168153004/diff/20001/content/browser/gpu/com...
content/browser/gpu/compositor_util.cc:212: // it uses its own thread, so reduce
the number of raster threads when async
So what about this stuff?
It sounds like it's talking about the transfer thread which is actually only
enabled on certain devices (see async_pixel_transfer_manager_android.cc). Plus
it will be going away entirely.

Q: Do we want to be subtracting a thread here if we are using 'idle uploads'?

[reveman, 2015-06-09 19:28:13]

https://codereview.chromium.org/1168153004/diff/20001/content/browser/gpu/com...
File content/browser/gpu/compositor_util.cc (right):

https://codereview.chromium.org/1168153004/diff/20001/content/browser/gpu/com...
content/browser/gpu/compositor_util.cc:212: // it uses its own thread, so reduce
the number of raster threads when async
On 2015/06/09 at 18:26:30, sievers wrote:
> So what about this stuff?
> It sounds like it's talking about the transfer thread which is actually only
enabled on certain devices (see async_pixel_transfer_manager_android.cc). Plus
it will be going away entirely.
> 
> Q: Do we want to be subtracting a thread here if we are using 'idle uploads'?

Not needed in that case but it's hard to know that from here. With async uploads
hopefully going away soon I don't think it's worth much time trying to improve
this.

[vmiura, 2015-06-09 22:02:07]

The CQ bit was checked by vmiura@chromium.org

[commit-bot: I haz the power, 2015-06-09 22:06:25]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1168153004/20001

[commit-bot: I haz the power, 2015-06-09 22:47:15]

Committed patchset #1 (id:20001)

[commit-bot: I haz the power, 2015-06-09 22:48:07]

Patchset 1 (id:??) landed as
https://crrev.com/6bfd5d8926aa101b39b0d3548b5dfd6cfad8b734
Cr-Commit-Position: refs/heads/master@{#333599}