linux-kernel - Re: [PATCH V4 07/14] perf/x86/intel: Support hardware TopDown metrics

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Date:   Mon, 30 Sep 2019 12:17:57 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 V4 07/14] perf/x86/intel: Support hardware TopDown metrics

On 9/30/2019 10:53 AM, Peter Zijlstra wrote:
> 
> After that, I think we can simply do something like:
> 
> icl_update_topdown_event(..)

We should call this function in x86_pmu_commit_txn()?
In intel_pmu_read_event(), we just simply return, when TXN_READ is set 
and is_topdown_count().

If so, it looks like we need add a per-cpu variable to store the topdown 
group events which user tries to read. Then we can update these events 
in x86_pmu_commit_txn(). The same method as Power does.

Is my understanding correct?

> {
> 	int idx = event->hwc.idx;
> 
> 	if (is_metric_idx(idx))
> 		return;
> 
> 	// must be FIXED_SLOTS

The FIXED_SLOTS may not be in the group.

Thanks,
Kan
> 
> 	/* do teh thing and update SLOTS and METRIC together */
> }
> 
> Hmmm?