linux-kernel - Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics

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Date:   Tue, 28 May 2019 14:56:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, mingo@...hat.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, jolsa@...nel.org, eranian@...gle.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com
Subject: Re: [PATCH 4/9] perf/x86/intel: Support hardware TopDown metrics

On Tue, May 21, 2019 at 02:40:50PM -0700, kan.liang@...ux.intel.com wrote:

> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
> index e9075d57853d..07ecfe75f0e6 100644
> --- a/arch/x86/events/core.c
> +++ b/arch/x86/events/core.c
> @@ -91,16 +91,20 @@ u64 x86_perf_event_update(struct perf_event *event)
>  					new_raw_count) != prev_raw_count)
>  		goto again;
>  
> -	/*
> -	 * Now we have the new raw value and have updated the prev
> -	 * timestamp already. We can now calculate the elapsed delta
> -	 * (event-)time and add that to the generic event.
> -	 *
> -	 * Careful, not all hw sign-extends above the physical width
> -	 * of the count.
> -	 */
> -	delta = (new_raw_count << shift) - (prev_raw_count << shift);
> -	delta >>= shift;
> +	if (unlikely(hwc->flags & PERF_X86_EVENT_UPDATE))
> +		delta = x86_pmu.metric_update_event(event, new_raw_count);
> +	else {
> +		/*
> +		 * Now we have the new raw value and have updated the prev
> +		 * timestamp already. We can now calculate the elapsed delta
> +		 * (event-)time and add that to the generic event.
> +		 *
> +		 * Careful, not all hw sign-extends above the physical width
> +		 * of the count.
> +		 */
> +		delta = (new_raw_count << shift) - (prev_raw_count << shift);
> +		delta >>= shift;
> +	}
>  
>  	local64_add(delta, &event->count);
>  	local64_sub(delta, &hwc->period_left);

> @@ -1186,6 +1194,9 @@ int x86_perf_event_set_period(struct perf_event *event)
>  	if (idx == INTEL_PMC_IDX_FIXED_BTS)
>  		return 0;
>  
> +	if (x86_pmu.set_period && x86_pmu.set_period(event))
> +		goto update_userpage;
> +
>  	/*
>  	 * If we are way outside a reasonable range then just skip forward:
>  	 */
> @@ -1234,6 +1245,7 @@ int x86_perf_event_set_period(struct perf_event *event)
>  			(u64)(-left) & x86_pmu.cntval_mask);
>  	}
>  
> +update_userpage:
>  	perf_event_update_userpage(event);
>  
>  	return ret;


*groan*.... that's pretty terrible.