From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gregory Haskins Subject: [PATCH v2 4/4] sched: use highest_prio.next to optimize pull operations Date: Wed, 03 Dec 2008 17:09:51 -0500 Message-ID: <20081203220951.11729.90528.stgit@dev.haskins.net> References: <20081203220628.11729.42174.stgit@dev.haskins.net> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: peterz@infradead.org, rostedt@goodmis.org, ghaskins@novell.com, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org To: mingo@elte.hu Return-path: In-Reply-To: <20081203220628.11729.42174.stgit@dev.haskins.net> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org We currently take the rq->lock for every cpu in an overload state during pull_rt_tasks(). However, we now have enough information via the highest_prio.[curr|next] fields to determine if there is any tasks of interest to warrant the overhead of the rq->lock, before we actually take it. So we use this information to reduce lock contention during the pull for the case where the source-rq doesnt have tasks that preempt the current task. Signed-off-by: Gregory Haskins --- kernel/sched_rt.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-) diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c index 7431d19..6072f24 100644 --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -1220,6 +1220,18 @@ static int pull_rt_task(struct rq *this_rq) continue; src_rq = cpu_rq(cpu); + + /* + * Don't bother taking the src_rq->lock if the next highest + * task is known to be lower-priority than our current task. + * This may look racy, but if this value is about to go + * logically higher, the src_rq will push this task away. + * And if its going logically lower, we do not care + */ + if (src_rq->rt.highest_prio.next >= + this_rq->rt.highest_prio.curr) + continue; + /* * We can potentially drop this_rq's lock in * double_lock_balance, and another CPU could