Messages in this thread | | | From | Song Liu <> | Subject | Re: [PATCH v2 1/1] perf: Sharing PMU counters across compatible events | Date | Tue, 11 Sep 2018 13:38:49 +0000 |
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> On Sep 10, 2018, at 1:15 AM, Jiri Olsa <jolsa@redhat.com> wrote: > > On Thu, Aug 30, 2018 at 06:51:07PM +0000, Song Liu wrote: >> >> >>> On Aug 30, 2018, at 8:18 AM, Jiri Olsa <jolsa@redhat.com> 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). > > yep, I understand.. still, it seems too much to allocate > the whole 'struct perf_even't just to get separated 'count' > variable
In theory, we only need separated counters. However, in practice, there are other variables we need to handle for a switch_master operation. For example, we need make sure event->state is always set properly. So this optimization is not easy to implement. How about we optimize it after this patch gets in?
Thanks, Song
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