Messages in this thread | | | Date | Fri, 5 Jun 2015 14:09:09 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH] sched: Fix sched_wakeup tracepoint |
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On Fri, Jun 05, 2015 at 01:41:49PM +0200, Mathieu Desnoyers wrote: > Commit 317f394160e9 "sched: Move the second half of ttwu() to the remote cpu" > moves ttwu_do_wakeup() to an IPI handler context on the remote CPU for > remote wakeups. This commit appeared upstream in Linux v3.0. > > Unfortunately, ttwu_do_wakeup() happens to contain the "sched_wakeup" > tracepoint. Analyzing wakup latencies depends on getting the wakeup > chain right: which process is the waker, which is the wakee. Moving this > instrumention outside of the waker context prevents trace analysis tools > from getting the waker pid, either through "current" in the tracepoint > probe, or by deducing it using other scheduler events based on the CPU > executing the tracepoint. > > Another side-effect of moving this instrumentation to the scheduler ipi > is that the delay during which the wakeup is sitting in the pending > queue is not accounted for when calculating wakeup latency. > > Therefore, move the sched_wakeup instrumentation back to the waker > context to fix those two shortcomings.
What do you consider wakeup-latency? I don't see how moving the tracepoint into the caller will magically account the queue time.
> +++ b/kernel/sched/core.c > @@ -1457,7 +1457,6 @@ static void > ttwu_do_wakeup(struct rq *rq, struct task_struct *p, int wake_flags) > { > check_preempt_curr(rq, p, wake_flags); > - trace_sched_wakeup(p, true); > > p->state = TASK_RUNNING; > #ifdef CONFIG_SMP > @@ -1505,6 +1504,7 @@ static int ttwu_remote(struct task_struct *p, int wake_flags) > if (task_on_rq_queued(p)) { > /* check_preempt_curr() may use rq clock */ > update_rq_clock(rq); > + trace_sched_wakeup(p, true); > ttwu_do_wakeup(rq, p, wake_flags); > ret = 1; > } > @@ -1619,6 +1619,7 @@ static void ttwu_queue(struct task_struct *p, int cpu) > { > struct rq *rq = cpu_rq(cpu); > > + trace_sched_wakeup(p, true); > #if defined(CONFIG_SMP) > if (sched_feat(TTWU_QUEUE) && !cpus_share_cache(smp_processor_id(), cpu)) { > sched_clock_cpu(cpu); /* sync clocks x-cpu */
You only need one site in try_to_wake_up(), put it right after success=1.
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