Messages in this thread | | | Date | Fri, 22 May 2015 14:53:44 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 02/10] perf/x86: Improve HT workaround GP counter constraint |
| |
On Fri, May 22, 2015 at 05:35:14AM -0700, Stephane Eranian wrote: > On Fri, May 22, 2015 at 4:28 AM, Peter Zijlstra <peterz@infradead.org> 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.
In any case, there's at least two more bugs in that patch that I know of, one of which I've fixed, the other I know how to fix.
Will re-post in a bit once I got it tested.
| |