Messages in this thread | | | Date | Wed, 15 Sep 2010 20:44:24 +0200 | From | Robert Richter <> | Subject | Re: [PATCH] perf, x86: catch spurious interrupts after disabling counters |
| |
On 15.09.10 13:32:49, Stephane Eranian wrote: > > I tried to clear the bit in the active_mask after disabling the > > counter (writing to the msr), which did not solve it. Shouldn't the > > counter be disabled immediatly? Maybe clearing the INT bit would have > > been worked too, but I was not sure about side effects. > > > 0 instr1 > 1 instr2 > 2 instr3 > 3 wrmsrl(eventsel0, 0); > > There is skid between the instruction you overflow the counter and > where the interrupt > is posted. If you overflow on instr1, suppose you post the interrupt > on instr3 which > is immediately followed by disable. There may a chance you get the > interrupt even > though the counter was disabled. I also don't know when the INT bit is > looked at.
Yes, this could be possible. So, we should assume interrupts may be delivered after a counter is disabled, which the patch addresses.
> > It may be worthwhile trying with: > > static inline void x86_pmu_disable_event(struct perf_event *event) > { > struct hw_perf_event *hwc = &event->hw; > (void)checking_wrmsrl(hwc->config_base + hwc->idx, 0); > } > > to see if it makes a difference. > > > >> Does the counter value reflect this? > > > > Yes, the disabled bit was cleared after reading the evntsel msr and > > the ctr value have had about 400 cycles (it could have been > > overflowed, though we actually can't say since the counter was > > disabled). > > > >> Were you also getting this if you were only measuring at the user level? > > > > I tried only > > > > perf record ./hackbench 10 > > > > which triggered it on my system. > > > I suspect that if you do: > > perf record -e cycles:u ./hackbench 10 > > It does not happen.
Do you know at which period the counters running for the following?
perf record ./hackbench 10 perf record -e cycles -e instructions -e cache-references \ -e cache-misses -e branch-misses -a -- <cmd>
I couldn't find something about this in the man page.
I will do some further investigations here, esp. with:
* compile order, * checking_wrmsrl(), * -e cycles:u
But I can not start with it before next week.
-Robert
-- Advanced Micro Devices, Inc. Operating System Research Center
-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |