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Date: Thu, 30 Aug 2018 18:51:07 +0000 From: Song Liu <songliubraving@...com> To: Jiri Olsa <jolsa@...hat.com> CC: lkml <linux-kernel@...r.kernel.org>, "lkp@...el.com" <lkp@...el.com>, Kernel Team <Kernel-team@...com>, Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Jiri Olsa <jolsa@...nel.org>, Alexey Budankov <alexey.budankov@...ux.intel.com> Subject: Re: [PATCH v2 1/1] perf: Sharing PMU counters across compatible events > On Aug 30, 2018, at 8:18 AM, Jiri Olsa <jolsa@...hat.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). 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
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