From: Kirill Tkhai <ktkhai@parallels.com>
Date: Wed, 20 Aug 2014 09:48:29 +0000 (+0400)
Subject: sched/fair: Remove double_lock_balance() from load_balance()
X-Git-Tag: fixes-against-v3.18-rc2~97^2~56
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=163122b7fcfa28c0e4a838fcc8043c616746802e;p=pandora-kernel.git

sched/fair: Remove double_lock_balance() from load_balance()

Avoid double_rq_lock() and use TASK_ON_RQ_MIGRATING for
load_balance(). The advantage is (obviously) not holding two
rq->lock's at the same time and thereby increasing parallelism.

Further note that if there was no task to migrate we will not
have acquired the second rq->lock at all.

The important point to note is that because we acquire dst->lock
immediately after releasing src->lock the potential wait time of
task_rq_lock() callers on TASK_ON_RQ_MIGRATING is not longer
than it would have been in the double rq lock scenario.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1408528109.23412.94.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---

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