linux-kernel - Re: [PATCH V6 07/14] perf/x86/intel: Generic support for hardware TopDown metrics

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Message-ID: <c814c39a-3cd2-f4d3-0b89-fbe4993e1fcc@linux.intel.com>
Date:   Mon, 20 Jul 2020 14:11:54 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 07/14] perf/x86/intel: Generic support for hardware
 TopDown metrics



On 7/20/2020 1:41 PM, Peter Zijlstra wrote:
> On Fri, Jul 17, 2020 at 07:05:47AM -0700, kan.liang@...ux.intel.com wrote:
> 
>> For the event mapping, a special 0x00 event code is used, which is
>> reserved for fake events. The metric events start from umask 0x10.
> 
>> +#define INTEL_PMC_IDX_METRIC_BASE		(INTEL_PMC_IDX_FIXED + 16)
>> +#define INTEL_PMC_IDX_TD_RETIRING		(INTEL_PMC_IDX_METRIC_BASE + 0)
>> +#define INTEL_PMC_IDX_TD_BAD_SPEC		(INTEL_PMC_IDX_METRIC_BASE + 1)
>> +#define INTEL_PMC_IDX_TD_FE_BOUND		(INTEL_PMC_IDX_METRIC_BASE + 2)
>> +#define INTEL_PMC_IDX_TD_BE_BOUND		(INTEL_PMC_IDX_METRIC_BASE + 3)
> 
> So this is internal and we can change it around if/when needed, right?
> 

Yes

>> +#define INTEL_PMC_IDX_METRIC_END		INTEL_PMC_IDX_TD_BE_BOUND
>> +#define INTEL_PMC_MSK_TOPDOWN			((0xfull << INTEL_PMC_IDX_METRIC_BASE) | \
>> +						INTEL_PMC_MSK_FIXED_SLOTS)
>> +
>> +/*
>> + * There is no event-code assigned to the TopDown events.
>> + *
>> + * For the slots event, use the pseudo code of the fixed counter 3.
>> + *
>> + * For the metric events, the pseudo event-code is 0x00.
>> + * The pseudo umask-code starts from 0x10.
>> + */
>> +#define INTEL_TD_SLOTS				0x0400	/* TOPDOWN.SLOTS */
>> +/* Level 1 metrics */
>> +#define INTEL_TD_METRIC_RETIRING		0x1000	/* Retiring metric */
>> +#define INTEL_TD_METRIC_BAD_SPEC		0x1100	/* Bad speculation metric */
>> +#define INTEL_TD_METRIC_FE_BOUND		0x1200	/* FE bound metric */
>> +#define INTEL_TD_METRIC_BE_BOUND		0x1300	/* BE bound metric */
>> +#define INTEL_TD_METRIC_MAX			INTEL_TD_METRIC_BE_BOUND
>> +#define INTEL_TD_METRIC_NUM			4
> 
> But this is ABI, once we merge this, it's stuck.
> 
> Also, per how Fixed2 is 0x0300, should not Fixed16 (aka
> METRICS_RETIRING) be 0x1100 ?
> 
> But aside of that, are we sure the hardware will never grow a Fixed16?
> Or do we want to be paranoid and move the metrics events up in the
> pseudo event space?
> 

Right, we cannot guarantee that the number of fixed counters is always 
less than 16.

I will move the metrics events to the middle of the pseudo event space.

+#define INTEL_TD_METRIC_RETIRING	0x8000	/* Retiring metric */
+#define INTEL_TD_METRIC_BAD_SPEC	0x8100	/* Bad speculation metric */
+#define INTEL_TD_METRIC_FE_BOUND	0x8200	/* FE bound metric */
+#define INTEL_TD_METRIC_BE_BOUND	0x8300	/* BE bound metric */

Thanks,
Kan