linux-kernel - Re: [PATCH v2 1/1] perf: Sharing PMU counters across compatible events

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Date:   Thu, 30 Aug 2018 17:18:10 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, lkp@...el.com, 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 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