> On Aug 30, 2018, at 8:18 AM, Jiri Olsa <[email protected]> wrote:
>
> On Wed, Aug 15, 2018 at 10:03:13AM -0700, Song Liu wrote:
>
> SNIP
>
>> @@ -6100,7 +6333,7 @@ static void perf_output_read_group(struct
>> perf_output_handle *handle,
>>
>> if ((sub != event) &&
>> (sub->state == PERF_EVENT_STATE_ACTIVE))
>> - sub->pmu->read(sub);
>> + event_pmu_read(sub);
>>
>> values[n++] = perf_event_count(sub);
>> if (read_format & PERF_FORMAT_ID)
>> @@ -9109,7 +9342,7 @@ static enum hrtimer_restart
>> perf_swevent_hrtimer(struct hrtimer *hrtimer)
>> if (event->state != PERF_EVENT_STATE_ACTIVE)
>> return HRTIMER_NORESTART;
>>
>> - event->pmu->read(event);
>> + event_pmu_read(event);
>>
>> perf_sample_data_init(&data, 0, event->hw.last_period);
>> regs = get_irq_regs();
>> @@ -10504,6 +10737,14 @@ SYSCALL_DEFINE5(perf_event_open,
>> goto err_cred;
>> }
>>
>> + if (perf_event_can_share(event)) {
>> + event->tmp_master = perf_event_alloc(&event->attr, cpu,
>> + task, NULL, NULL,
>> + NULL, NULL, -1);
>
> can't get around this.. I understand the need, but AFAICS you allocate
> the whole 'struct perf_event', just because there's count field in it
> otherwise the 'struct hw_perf_event' should be enough to carry all that's
> needed to read hw event
>
> would it be better to move the count to 'struct hw_perf_event' and use
> that instead? assuming I'm not missing anything..
>
> jirka
I am trying to make the master event function the same as a real event,
while keep dup events as followers. This avoids "switching master" in
earlier versions (and Tejun's RFC).
I also read your version that does it at hardware level, and found it
simplifies some parts of the change. I picked current approach mostly
because this approach keeps all logic about PMU sharing in one place,
and the rest of the perf subsystem can stay as-is. If this approach
doesn't work out, I will probably try the hardware level approach.
Thanks,
Song
