On Fri, May 22, 2015 at 05:55:32AM -0700, Stephane Eranian wrote: > On Fri, May 22, 2015 at 5:53 AM, Peter Zijlstra <[email protected]> wrote: > > On Fri, May 22, 2015 at 05:35:14AM -0700, Stephane Eranian wrote: > >> On Fri, May 22, 2015 at 4:28 AM, Peter Zijlstra <[email protected]> > >> wrote: > >> > On Fri, May 22, 2015 at 01:21:46PM +0200, Peter Zijlstra wrote: > >> >> @@ -821,8 +828,24 @@ int x86_schedule_events(struct cpu_hw_ev > >> >> > >> >> /* slow path */ > >> >> if (i != n) { > >> >> + int gpmax = x86_pmu.num_counters / 2; > >> >> + > >> >> + /* > >> >> + * Do not allow scheduling of more than half the available > >> >> + * generic counters. > >> >> + * > >> >> + * This helps avoid counter starvation of sibling thread > >> >> by > >> >> + * ensuring at most half the counters cannot be in > >> >> exclusive > >> >> + * mode. There is no designated counters for the limits. > >> >> Any > >> >> + * N/2 counters can be used. This helps with events with > >> >> + * specific counter constraints. > >> >> + */ > >> >> + if (is_ht_workaround_enabled() && !cpuc->is_fake && > >> >> + READ_ONCE(cpuc->excl_cntrs->exclusive_present)) > >> >> + gpmax /= 2; > >> >> + > >> >> unsched = perf_assign_events(cpuc->event_constraint, n, > >> >> wmin, > >> >> - wmax, assign); > >> >> + wmax, gpmax, assign); > >> >> } > >> >> > >> > > >> > Hmm, I divide by 2 twice.. no wonder it doesn't quite work as expected. > >> > >> Yes, that's what I said. Other problem is, with no watchdog, measuring > >> a non-corrupting event is still multiplexing when more than 2 instances > >> are passed: > >> $ perf stat -a -C 0 -e r20cc,r20cc,r20cc,r20cc -I 1000 sleep 100 > >> > >> I get 50% scheduling, only 2 out of 4 events scheduled at any time. > >> > >> There is nothing running on the sibling thread, so it should let me run > >> with 4 > >> instances as per your patch. > > > > Ah, I limited it to n/2 if either of the siblings has an exclusive event > > on. > > > But in my test case above, there was no exclusive event at all on either > sibling and yet it limited the non-excl to 2.
I bet you tested the exclusive events earlier :-) Its one of the bugs, the n_excl accounting is leaking up. Once !0 it stays !0. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
