On Fri, May 22, 2015 at 6:05 AM, Stephane Eranian <[email protected]> wrote: > On Fri, May 22, 2015 at 5:59 AM, Peter Zijlstra <[email protected]> wrote: >> 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. > > So you're saying intel_put_excl_constraint() does not do the --n_excl? > Could it be that the flags is not showing PERF_X86_EVENT_EXCL? > Cannot be related to cpuc_fake because you have it in both the ++ > and -- functions.
One other thing I noticed is that the --n_excl needs to be protected by the excl_cntrs->lock in put_excl_constraints(). -- 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/
