linux-kernel - Re: [PATCH V6 09/14] perf/x86/intel: Support TopDown metrics on Ice Lake

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Message-ID: <20200721143110.GL119549@hirez.programming.kicks-ass.net>
Date:   Tue, 21 Jul 2020 16:31:10 +0200
From:   peterz@...radead.org
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     acme@...hat.com, mingo@...nel.org, linux-kernel@...r.kernel.org,
        jolsa@...nel.org, eranian@...gle.com,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com
Subject: Re: [PATCH V6 09/14] perf/x86/intel: Support TopDown metrics on Ice
 Lake

On Tue, Jul 21, 2020 at 10:23:36AM -0400, Liang, Kan wrote:

> Patch 13 forces the slots event to be part of a metric group. In patch 7,
> for a metric group, we only update the values once with slots event.
> I think the normal case mentioned above should not happen.
> 
> +	/* Only need to call update_topdown_event() once for group read. */
> +	if ((cpuc->txn_flags & PERF_PMU_TXN_READ) &&
> +	    !is_slots_event(event))
> +		return;
> +
> +	perf_pmu_disable(event->pmu);
> +	x86_pmu.update_topdown_event(event);
> +	perf_pmu_enable(event->pmu);

Ah, I missed that.

That also requires SLOTS to be the leader so that it will be the first
read. Did we enforce that somewhere?