From: Srivatsa Vaddagiri Date: Sat, 17 Sep 2016 01:28:51 +0000 (-0700) Subject: sched/fair: Fix SCHED_HRTICK bug leading to late preemption of tasks X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=8bf46a39be910937d4c9e8d999a7438a7ae1a75b;p=openwrt%2Fstaging%2Fblogic.git sched/fair: Fix SCHED_HRTICK bug leading to late preemption of tasks SCHED_HRTICK feature is useful to preempt SCHED_FAIR tasks on-the-dot (just when they would have exceeded their ideal_runtime). It makes use of a per-CPU hrtimer resource and hence arming that hrtimer should be based on total SCHED_FAIR tasks a CPU has across its various cfs_rqs, rather than being based on number of tasks in a particular cfs_rq (as implemented currently). As a result, with current code, its possible for a running task (which is the sole task in its cfs_rq) to be preempted much after its ideal_runtime has elapsed, resulting in increased latency for tasks in other cfs_rq on same CPU. Fix this by arming sched hrtimer based on total number of SCHED_FAIR tasks a CPU has across its various cfs_rqs. Signed-off-by: Srivatsa Vaddagiri Signed-off-by: Joonwoo Park Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1474075731-11550-1-git-send-email-joonwoop@codeaurora.org Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 986c10c25176..8fb4d1942c14 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4469,7 +4469,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p) WARN_ON(task_rq(p) != rq); - if (cfs_rq->nr_running > 1) { + if (rq->cfs.h_nr_running > 1) { u64 slice = sched_slice(cfs_rq, se); u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime; s64 delta = slice - ran;