On Tuesday 17 November 2015 04:37 PM, Peter Zijlstra wrote:
> On Tue, Nov 17, 2015 at 09:14:59AM +0000, Vineet Gupta wrote:
>> > Let's check with Peter as I'm not sure how exactly the read call will
>> > nest for same counter on same core ?
> Various possible ways, but the easiest is userspace doing a sys_read()
> on the counter while the NMI happens.
>
>
That means Alexey need to revert the hunk ?
static void arc_perf_event_update(struct perf_event *event,
struct hw_perf_event *hwc, int idx)
{
- uint64_t prev_raw_count, new_raw_count;
- int64_t delta;
-
- do {
- prev_raw_count = local64_read(&hwc->prev_count);
- new_raw_count = arc_pmu_read_counter(idx);
- } while (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
- new_raw_count) != prev_raw_count);
-
- delta = (new_raw_count - prev_raw_count) &
- ((1ULL << arc_pmu->counter_size) - 1ULL);
+ uint64_t prev_raw_count = local64_read(&hwc->prev_count);
+ uint64_t new_raw_count = arc_pmu_read_counter(idx);
+ int64_t delta = new_raw_count - prev_raw_count;
+ /*
+ * We don't afaraid of hwc->prev_count changing beneath our feet
+ * because there's no way for us to re-enter this function anytime.
+ */
+ local64_set(&hwc->prev_count, new_raw_count);
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