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SubjectRe: [PATCH v6 2/3]: perf/core: use context tstamp_data for skipped events on mux interrupt
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On 03.08.2017 18:00, Peter Zijlstra wrote:
> On Wed, Aug 02, 2017 at 11:15:39AM +0300, Alexey Budankov wrote:
>> @@ -772,6 +780,10 @@ struct perf_event_context {
>> */
>> u64 time;
>> u64 timestamp;
>> + /*
>> + * Context cache for filtered out events;
>> + */
>> + struct perf_event_tstamp tstamp_data;
>>
>> /*
>> * These fields let us detect when two contexts have both
>
>
>> @@ -1379,6 +1379,9 @@ static void update_context_time(struct perf_event_context *ctx)
>>
>> ctx->time += now - ctx->timestamp;
>> ctx->timestamp = now;
>> +
>> + ctx->tstamp_data.running += ctx->time - ctx->tstamp_data.stopped;
>> + ctx->tstamp_data.stopped = ctx->time;
>> }
>>
>> static u64 perf_event_time(struct perf_event *event)
>
> It appears to me we have some redundancy here.
>
>
>> @@ -1968,9 +1971,13 @@ event_sched_out(struct perf_event *event,
>> */
>> if (event->state == PERF_EVENT_STATE_INACTIVE &&
>> !event_filter_match(event)) {
>> + delta = tstamp - event->tstamp->stopped;
>> + event->tstamp->running += delta;
>> + event->tstamp->stopped = tstamp;
>> + if (event->tstamp != &event->tstamp_data) {
>> + event->tstamp_data = *event->tstamp;
>
> This,
>
>> + event->tstamp = &event->tstamp_data;
>> + }
>> }
>>
>> if (event->state != PERF_EVENT_STATE_ACTIVE)
>
>
>> @@ -3239,8 +3246,11 @@ ctx_pinned_sched_in(struct perf_event *event, void *data)
>>
>> if (event->state <= PERF_EVENT_STATE_OFF)
>> return 0;
>> - if (!event_filter_match(event))
>> + if (!event_filter_match(event)) {
>> + if (event->tstamp != &params->ctx->tstamp_data)
>> + event->tstamp = &params->ctx->tstamp_data;
>
> this and
>
>> return 0;
>> + }
>>
>> /* may need to reset tstamp_enabled */
>> if (is_cgroup_event(event))
>> @@ -3273,8 +3283,11 @@ ctx_flexible_sched_in(struct perf_event *event, void *data)
>> * Listen to the 'cpu' scheduling filter constraint
>> * of events:
>> */
>> - if (!event_filter_match(event))
>> + if (!event_filter_match(event)) {
>> + if (event->tstamp != &params->ctx->tstamp_data)
>> + event->tstamp = &params->ctx->tstamp_data;
>
> this..
>
>> return 0;
>> + }
>>
>> /* may need to reset tstamp_enabled */
>> if (is_cgroup_event(event))
>
>
> Are the magic spots, right? And I'm not convinced its right.
>
> Suppose I have two events in my context, and I created them 1 minute
> apart. Then their respective tstamp_enabled are 1 minute apart as well.
> But the above doesn't seem to preserve that difference.
>
> A similar argument can be made for running I think. That is a per event
> value and cannot be passed along to the ctx and back.

Aww, I see your point and it challenges my initial assumptions.
Let me think thru the case more. There must be some solution. Thanks!

>
>
>

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