From: Steven Rostedt <rostedt@goodmis.org>
To: tip-bot for Tim Chen <tipbot@zytor.com>
Cc: suruchi.a.kadu@intel.com, linux-kernel@vger.kernel.org,
sbohrer@rgmadvisors.com, peterz@infradead.org, mingo@kernel.org,
tglx@linutronix.de, doug.nelson@intel.com,
torvalds@linux-foundation.org, tim.c.chen@linux.intel.com,
hpa@zytor.com, stable@vger.kernel.org,
Clark Williams <williams@redhat.com>
Subject: Re: [tip:sched/core] sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target
Date: Tue, 24 Feb 2015 11:12:47 -0500 [thread overview]
Message-ID: <20150224111247.2ca122c3@gandalf.local.home> (raw)
In-Reply-To: <tip-80e3d87b2c5582db0ab5e39610ce3707d97ba409@git.kernel.org>
On Sun, 1 Feb 2015 09:52:24 -0800
tip-bot for Tim Chen <tipbot@zytor.com> wrote:
> Commit-ID: 80e3d87b2c5582db0ab5e39610ce3707d97ba409
> Gitweb: http://git.kernel.org/tip/80e3d87b2c5582db0ab5e39610ce3707d97ba409
> Author: Tim Chen <tim.c.chen@linux.intel.com>
> AuthorDate: Fri, 12 Dec 2014 15:38:12 -0800
> Committer: Ingo Molnar <mingo@kernel.org>
> CommitDate: Fri, 30 Jan 2015 19:38:49 +0100
>
> sched/rt: Reduce rq lock contention by eliminating locking of non-feasible target
>
> This patch adds checks that prevens futile attempts to move rt tasks
> to a CPU with active tasks of equal or higher priority.
>
> This reduces run queue lock contention and improves the performance of
> a well known OLTP benchmark by 0.7%.
>
> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Shawn Bohrer <sbohrer@rgmadvisors.com>
> Cc: Suruchi Kadu <suruchi.a.kadu@intel.com>
> Cc: Doug Nelson<doug.nelson@intel.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Link: http://lkml.kernel.org/r/1421430374.2399.27.camel@schen9-desk2.jf.intel.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
I see this has been added to mainline already. I think this should go
to stable as well. As far back as it applies. I'll even add this to the
stable-rt if need be. But I rather pull it into stable-rt via the
stable branches.
Thanks,
-- Steve
> ---
> kernel/sched/rt.c | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 6725e3c..f4d4b07 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1340,7 +1340,12 @@ select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)
> curr->prio <= p->prio)) {
> int target = find_lowest_rq(p);
>
> - if (target != -1)
> + /*
> + * Don't bother moving it if the destination CPU is
> + * not running a lower priority task.
> + */
> + if (target != -1 &&
> + p->prio < cpu_rq(target)->rt.highest_prio.curr)
> cpu = target;
> }
> rcu_read_unlock();
> @@ -1617,6 +1622,16 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
>
> lowest_rq = cpu_rq(cpu);
>
> + if (lowest_rq->rt.highest_prio.curr <= task->prio) {
> + /*
> + * Target rq has tasks of equal or higher priority,
> + * retrying does not release any lock and is unlikely
> + * to yield a different result.
> + */
> + lowest_rq = NULL;
> + break;
> + }
> +
> /* if the prio of this runqueue changed, try again */
> if (double_lock_balance(rq, lowest_rq)) {
> /*
next prev parent reply other threads:[~2015-02-24 16:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-06 19:01 [PATCH] Repost sched-rt: Reduce rq lock contention by eliminating locking of non-feasible target Tim Chen
2015-01-06 19:30 ` Peter Zijlstra
2015-01-15 17:13 ` Tim Chen
2015-01-16 1:58 ` Steven Rostedt
2015-01-16 17:46 ` Tim Chen
2015-01-22 17:48 ` Tim Chen
2015-02-01 17:52 ` [tip:sched/core] sched/rt: " tip-bot for Tim Chen
2015-02-24 16:12 ` Steven Rostedt [this message]
2015-03-03 21:12 ` Ben Hutchings
2015-04-09 1:17 ` Zefan Li
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