----- On Jun 5, 2015, at 2:32 PM, Thomas Gleixner t...@linutronix.de wrote:
> On Fri, 5 Jun 2015, Peter Zijlstra wrote: >> 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. > > Well, the point of wakeup is when the wakee calls wakeup. If the trace ^ I think you actually mean "when the waker calls wakeup". > point is in the IPI then you account the time between the wakeup and > the actuall handling in the IPI to the wakee instead of accounting it > to the time between wakeup and sched switch. > Thanks, Mathieu > Thanks, > > tglx -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
