Commit-ID: 8bf46a39be910937d4c9e8d999a7438a7ae1a75b Gitweb: http://git.kernel.org/tip/8bf46a39be910937d4c9e8d999a7438a7ae1a75b Author: Srivatsa Vaddagiri <[email protected]> AuthorDate: Fri, 16 Sep 2016 18:28:51 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Thu, 22 Sep 2016 15:20:18 +0200
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 <[email protected]> Signed-off-by: Joonwoo Park <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 986c10c..8fb4d19 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;
