Oilpan: Scale up the number of marking threads according to available processors

Oilpan: Scale up the number of marking threads according to available processors

Currently we use 2 marking threads regardless of the number of processors available.
Given that the marking phase takes a substantial amount of time,
this CL changes the number of marking threads to min(the number of processors, 4).

This CL also decreases the block size of each CallStack from 200 to 128
because load balancing is not good in some benchmarks such as LargeDistributionWithoutLayout. This CL improves LargeDistributionWithoutLayout by 10% for example.

BUG=420515
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=183613

[haraken, 2014-10-10 07:50:37]

haraken@chromium.org changed reviewers:
+ oilpan-reviews@chromium.org

[haraken, 2014-10-10 09:13:51]

PTAL

[sof, 2014-10-13 08:05:20]

sigbjornf@opera.com changed reviewers:
+ sigbjornf@opera.com

[sof, 2014-10-13 08:05:21]

lgtm, let's try this.

A worry is that the fan out is too aggressive on power-conscious targets.

[haraken, 2014-10-13 15:21:27]

> A worry is that the fan out is too aggressive on power-conscious targets.

I decreased the number of marking threads from 8 to 4. I think we should try to
make the load balance better before trying to increase the number of threads :)

[haraken, 2014-10-13 15:21:40]

The CQ bit was checked by haraken@chromium.org

[commit-bot: I haz the power, 2014-10-13 15:21:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/648633002/170001

[commit-bot: I haz the power, 2014-10-13 16:29:19]

Committed patchset #6 (id:170001) as 183613