Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v2 1/3] sched/fair: Avoid redundant idle_cpu() call in update_sg_lb_stats() | Date | Wed, 2 Dec 2015 13:41:48 -0500 |
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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> --- kernel/sched/fair.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f04fda8..8f1eccc 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6302,7 +6302,7 @@ 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)); @@ -6319,7 +6319,8 @@ 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 @@ -6327,7 +6328,10 @@ 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++; } -- 1.7.1
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