Messages in this thread | | | Subject | Re: [PATCHv2 3/4] arm-cci: Add routines to enable/disable all counters | From | "Suzuki K. Poulose" <> | Date | Thu, 5 Nov 2015 17:52:37 +0000 |
| |
On 05/11/15 17:27, Mark Rutland wrote: >>> Can we not get rid of the mask entirely? The combination of used_mask >>> and each event's hwc->state tells us which counters are actually in use. >> >> The problem is that neither hwc->state nor the cci_pmu->hw_events->events is >> protected by pmu_lock, while enable/disable counter is. So we cannot really >> rely on ((struct perf_event *)(cci_pmu->hw_events->events[counter]))->hw->state. > > They must be protected somehow, or we'd have races against cross-calls > and/or the interrupt handler.
> > Are we protected due to being cpu-affine with interrupts disabled when > modifying these, is there some other mechanism that protects us, or do > we have additional problems here? >
Each perf_event is allocated a counter id atomically using the bit mask. So, once the id is allocated nobody messes with that id from the PMU side. And, the hw->state may have its own protection within the generic perf layer(which I haven't checked).
Thanks Suzuki
| |