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 <vatsa@codeaurora.org> Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1474075731-11550-1-git-send-email-joonwoop@codeaurora.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -4469,7 +4469,7 @@ static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
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WARN_ON(task_rq(p) != rq);
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WARN_ON(task_rq(p) != rq);
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if (cfs_rq->nr_running > 1) {
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if (rq->cfs.h_nr_running > 1) {
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u64 slice = sched_slice(cfs_rq, se);
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u64 slice = sched_slice(cfs_rq, se);
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u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
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u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
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s64 delta = slice - ran;
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s64 delta = slice - ran;
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