On Wed, Jun 4, 2014 at 6:00 AM, Daniel Lezcano <daniel.lezc...@linaro.org> wrote: > On 06/04/2014 02:29 AM, Andy Lutomirski wrote: >> >> Remote wakeups of polling CPUs are a valuable performance >> improvement; add a tracepoint to make it much easier to verify that >> they're working. >> >> Signed-off-by: Andy Lutomirski <l...@amacapital.net> > > > I don't think this trace makes sense. The polling state is x86 only and this > trace is in the generic code. > > Furthermore, you may be not in polling state but in the idle mainloop before > or after the idle state, so the trace will be wrong for the purpose you are > aiming. > > IMO, the right place would be in 'poll_idle' but why add such trace ? > > If, on x86, we exit poll_idle, we have the idle state exit trace. The > missing information would be the origin of the 'wakeup' (irq or ipi or > nothing). The missing informations are the IPI traces [1]. > > And as a sidenote, the polling state could be rare on a system with a > cpuidle driver, it should be much more easy to restrict the idle states to > 'poll' only and check there are no IPI_WAKEUP, no ?
While developing and testing this, I found it quite useful to measure the ratio of IPIs to non-IPIs. I think most of your objection stems from the fact that I named this tracepoint rather poorly. How about "sched_wake_idle_without_ipi"? I don't think there's anywhere good to put it in arch / cpuidle driver code (neither the true polling loop nor (AFAIK) x86 mwait the sleeping cpu any straightforward indication of why it woke up. On archs without TIF_POLLING_NRFLAG, the compiler should optimize this away completely. On archs with TIF_POLLING_NRFLAG but not actual polling, it could be interesting to see if this tracepoint ever hits and, if not, consider removing TIF_POLLING_NRFLAG. --Andy -- 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/
