On Sun, 1 Feb 2015 09:52:24 -0800 tip-bot for Tim Chen <tipbot@xxxxxxxxx> wrote: > Commit-ID: 80e3d87b2c5582db0ab5e39610ce3707d97ba409 > Gitweb: http://git.kernel.org/tip/80e3d87b2c5582db0ab5e39610ce3707d97ba409 > Author: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> > AuthorDate: Fri, 12 Dec 2014 15:38:12 -0800 > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > 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@xxxxxxxxxxxxxxx> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Cc: Shawn Bohrer <sbohrer@xxxxxxxxxxxxxxx> > Cc: Suruchi Kadu <suruchi.a.kadu@xxxxxxxxx> > Cc: Doug Nelson<doug.nelson@xxxxxxxxx> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Link: http://lkml.kernel.org/r/1421430374.2399.27.camel@xxxxxxxxxxxxxxxxxxxxxxxxx > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> 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)) { > /* -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html