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. -- 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/
