On Tue, Jun 19, 2018 at 11:15:39AM +0100, Suzuki K Poulose wrote: > The armpmu uses get_event_idx callback to allocate an event > counter for a given event, which marks the selected counter > as "used". Now, when we delete the counter, the arm_pmu goes > ahead and clears the "used" bit and then invokes the "clear_event_idx" > call back, which kind of splits the job between the core code > and the backend. Tidy this up by relying on the clear_event_idx > to do the book keeping, if available. Otherwise, let the core > driver do the default "clear" bit operation. This will be useful > for adding the chained event support, where we leave the event > idx maintenance to the backend. > > Also, when an event is removed from the PMU, reset the hw.idx > to indicate that a counter is not allocated for this event, > to help the backends do better checks. This will be also used > for the chain counter support. > > Cc: Mark Rutland <[email protected]> > Cc: Will Deacon <[email protected]> > Reviewed-by: Julien Thierry <[email protected]> > Signed-off-by: Suzuki K Poulose <[email protected]> > --- > Changes since v2: > - Reset the event counter after an event is removed. > --- > arch/arm/kernel/perf_event_v7.c | 2 ++ > drivers/perf/arm_pmu.c | 17 +++++++++++++---- > 2 files changed, 15 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c > index fd7ce01..765d265 100644 > --- a/arch/arm/kernel/perf_event_v7.c > +++ b/arch/arm/kernel/perf_event_v7.c > @@ -1637,6 +1637,7 @@ static void krait_pmu_clear_event_idx(struct > pmu_hw_events *cpuc, > bool venum_event = EVENT_VENUM(hwc->config_base); > bool krait_event = EVENT_CPU(hwc->config_base); > > + clear_bit(hwc->idx, cpuc->used_mask); > if (venum_event || krait_event) { > bit = krait_event_to_bit(event, region, group); > clear_bit(bit, cpuc->used_mask); > @@ -1966,6 +1967,7 @@ static void scorpion_pmu_clear_event_idx(struct > pmu_hw_events *cpuc, > bool venum_event = EVENT_VENUM(hwc->config_base); > bool scorpion_event = EVENT_CPU(hwc->config_base); > > + clear_bit(hwc->idx, cpuc->used_mask); > if (venum_event || scorpion_event) { > bit = scorpion_event_to_bit(event, region, group); > clear_bit(bit, cpuc->used_mask);
As an aside, I think there's an existing problem with krait and cpu_pm_pmu_setup(), and we'll end up with the same issue when chained counters use multiple counters for one event. The krait code sets multiple bits in the PMU's pmu_hw_events::used_mask, but only one of these will have a corresponding (non-NULL) entry in pmu_hw_events::events[]. In cpu_pm_pmu_setup(), when we find the auxilliary counter associated with an event, its bit will be set in used_mask, but the pointer will be NULL, and that will blow up in start/stop. We can't just set multiple slots to point at the same counter, or we'd try to start/stop an event multiple times, which would also be bad. I guess the best thing to do would be to avoid the test_bit(), and just skip an idx if hw_events->events[idx] is NULL. Would you mind spinning a patch to that effect? Thanks, Mark.
