The prev_count needs setting when changing the counter value, otherwise
the calculated delta will be wrong, which for frequency sampling
(dynamic period sampling) results in sampling at too high a frequency.
For non-interrupting performance counters it should also be cleared when
enabling the counter since the write to the PERF_COUNT register will
clear the perf counter.
This also includes a minor change to remove the u64 cast from the
metag_pmu->write() call as metag_pmu->write() takes a u32 anyway, and in
any case GCC is smart enough to optimise away the cast.
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
if (left > (s64)metag_pmu->max_period)
left = metag_pmu->max_period;
if (left > (s64)metag_pmu->max_period)
left = metag_pmu->max_period;
- if (metag_pmu->write)
- metag_pmu->write(idx, (u64)(-left) & MAX_PERIOD);
+ if (metag_pmu->write) {
+ local64_set(&hwc->prev_count, -(s32)left);
+ metag_pmu->write(idx, -left & MAX_PERIOD);
+ }
perf_event_update_userpage(event);
perf_event_update_userpage(event);
* set to a specific value that needs preserving.
*/
tmp |= metag_in32(PERF_COUNT(idx)) & 0x00ffffff;
* set to a specific value that needs preserving.
*/
tmp |= metag_in32(PERF_COUNT(idx)) & 0x00ffffff;
+ else
+ /*
+ * Older cores reset the counter on write, so prev_count needs
+ * resetting too so we can calculate a correct delta.
+ */
+ local64_set(&event->prev_count, 0);
metag_out32(tmp, PERF_COUNT(idx));
unlock:
metag_out32(tmp, PERF_COUNT(idx));
unlock: