From: Paul Turner <pjt@google.com>
Date: Sat, 22 Jan 2011 04:45:03 +0000 (-0800)
Subject: sched: Avoid expensive initial update_cfs_load()
X-Git-Tag: v2.6.39-rc1~509^2~27
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f07333bf6ee66d9b49286cec4371cf375e745b7a;p=pandora-kernel.git

sched: Avoid expensive initial update_cfs_load()

Since cfs->{load_stamp,load_last} are zero-initalized the initial load update
will consider the delta to be 'since the beginning of time'.

This results in a lot of pointless divisions to bring this large period to be
within the sysctl_sched_shares_window.

Fix this by initializing load_stamp to be 1 at cfs_rq initialization, this
allows for an initial load_stamp > load_last which then lets standard idle
truncation proceed.

We avoid spinning (and slightly improve consistency) by fixing delta to be
[period - 1] in this path resulting in a slightly more predictable shares ramp.
(Previously the amount of idle time preserved by the overflow would range between
[period/2,period-1].)

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110122044852.102126037@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

Reading git-diff-tree failed