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authorWaiman Long <Waiman.Long@hpe.com>2015-11-25 14:09:38 -0500
committerIngo Molnar <mingo@kernel.org>2015-12-04 10:34:47 +0100
commita426f99c91d1036767a7819aaaba6bd3191b7f06 (patch)
treed47b87b2576ebb2618144dd2f6416a0c8e36efd8
parented82b8a1ff76ed7b2709e36ed361ddd022fe2407 (diff)
downloadlinux-a426f99c91d1036767a7819aaaba6bd3191b7f06.tar.bz2
sched/fair: Avoid redundant idle_cpu() call in update_sg_lb_stats()
Part of the responsibility of the update_sg_lb_stats() function is to update the idle_cpus statistical counter in struct sg_lb_stats. This check is done by calling idle_cpu(). The idle_cpu() function, in turn, checks a number of fields within the run queue structure such as rq->curr and rq->nr_running. With the current layout of the run queue structure, rq->curr and rq->nr_running are in separate cachelines. The rq->curr variable is checked first followed by nr_running. As nr_running is also accessed by update_sg_lb_stats() earlier, it makes no sense to load another cacheline when nr_running is not 0 as idle_cpu() will always return false in this case. This patch eliminates this redundant cacheline load by checking the cached nr_running before calling idle_cpu(). Signed-off-by: Waiman Long <Waiman.Long@hpe.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Douglas Hatch <doug.hatch@hpe.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Scott J Norton <scott.norton@hpe.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1448478580-26467-2-git-send-email-Waiman.Long@hpe.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--kernel/sched/fair.c10
1 files changed, 7 insertions, 3 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index efd664c4926e..4b0e8b8700fd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6398,7 +6398,7 @@ static inline void update_sg_lb_stats(struct lb_env *env,
bool *overload)
{
unsigned long load;
- int i;
+ int i, nr_running;
memset(sgs, 0, sizeof(*sgs));
@@ -6415,7 +6415,8 @@ static inline void update_sg_lb_stats(struct lb_env *env,
sgs->group_util += cpu_util(i);
sgs->sum_nr_running += rq->cfs.h_nr_running;
- if (rq->nr_running > 1)
+ nr_running = rq->nr_running;
+ if (nr_running > 1)
*overload = true;
#ifdef CONFIG_NUMA_BALANCING
@@ -6423,7 +6424,10 @@ static inline void update_sg_lb_stats(struct lb_env *env,
sgs->nr_preferred_running += rq->nr_preferred_running;
#endif
sgs->sum_weighted_load += weighted_cpuload(i);
- if (idle_cpu(i))
+ /*
+ * No need to call idle_cpu() if nr_running is not 0
+ */
+ if (!nr_running && idle_cpu(i))
sgs->idle_cpus++;
}