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authorJason Low <jason.low2@hp.com>2014-04-24 03:30:35 +0200
committerIngo Molnar <mingo@kernel.org>2014-05-07 13:33:53 +0200
commit39a4d9ca77a31503c6317e49742341d0859d5cb2 (patch)
treed45517454f4823a8a0d6599837d22419076162fa /kernel/sched
parentsched, ARM: Create a dedicated scheduler topology table (diff)
downloadlinux-39a4d9ca77a31503c6317e49742341d0859d5cb2.tar.xz
linux-39a4d9ca77a31503c6317e49742341d0859d5cb2.zip
sched/fair: Stop searching for tasks in newidle balance if there are runnable tasks
It was found that when running some workloads (such as AIM7) on large systems with many cores, CPUs do not remain idle for long. Thus, tasks can wake/get enqueued while doing idle balancing. In this patch, while traversing the domains in idle balance, in addition to checking for pulled_task, we add an extra check for this_rq->nr_running for determining if we should stop searching for tasks to pull. If there are runnable tasks on this rq, then we will stop traversing the domains. This reduces the chance that idle balance delays a task from running. This patch resulted in approximately a 6% performance improvement when running a Java Server workload on an 8 socket machine. Signed-off-by: Jason Low <jason.low2@hp.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: daniel.lezcano@linaro.org Cc: alex.shi@linaro.org Cc: preeti@linux.vnet.ibm.com Cc: efault@gmx.de Cc: vincent.guittot@linaro.org Cc: morten.rasmussen@arm.com Cc: aswin@hp.com Cc: chegu_vinod@hp.com Link: http://lkml.kernel.org/r/1398303035-18255-4-git-send-email-jason.low2@hp.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/fair.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 051903f33eec..28ccf502c63c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6713,7 +6713,6 @@ static int idle_balance(struct rq *this_rq)
if (sd->flags & SD_BALANCE_NEWIDLE) {
t0 = sched_clock_cpu(this_cpu);
- /* If we've pulled tasks over stop searching: */
pulled_task = load_balance(this_cpu, this_rq,
sd, CPU_NEWLY_IDLE,
&continue_balancing);
@@ -6728,7 +6727,12 @@ static int idle_balance(struct rq *this_rq)
interval = msecs_to_jiffies(sd->balance_interval);
if (time_after(next_balance, sd->last_balance + interval))
next_balance = sd->last_balance + interval;
- if (pulled_task)
+
+ /*
+ * Stop searching for tasks to pull if there are
+ * now runnable tasks on this rq.
+ */
+ if (pulled_task || this_rq->nr_running > 0)
break;
}
rcu_read_unlock();