linux-kernel - Re: [PATCH 2/9] perf/x86/intel: Basic support for metrics counters

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Message-ID: <dfaeb4b4-bf49-593d-b9e4-33dd8c050d4e@linux.intel.com>
Date:   Wed, 29 May 2019 10:40:52 -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 2/9] perf/x86/intel: Basic support for metrics counters



On 5/29/2019 3:28 AM, Peter Zijlstra wrote:
> On Tue, May 28, 2019 at 02:21:49PM -0400, Liang, Kan wrote:
>>
>>
>> On 5/28/2019 8:15 AM, Peter Zijlstra wrote:
>>> On Tue, May 21, 2019 at 02:40:48PM -0700, kan.liang@...ux.intel.com wrote:
>>>> +/*
>>>> + * We model PERF_METRICS as more magic fixed-mode PMCs, one for each metric
>>>> + * and another for the whole slots counter
>>>> + *
>>>> + * Internally they all map to Fixed Ctr 3 (SLOTS), and allocate PERF_METRICS
>>>> + * as an extra_reg. PERF_METRICS has no own configuration, but we fill in
>>>> + * the configuration of FxCtr3 to enforce that all the shared users of SLOTS
>>>> + * have the same configuration.
>>>> + */
>>>> +#define INTEL_PMC_IDX_FIXED_METRIC_BASE		(INTEL_PMC_IDX_FIXED + 17)
>>>> +#define INTEL_PMC_IDX_TD_RETIRING		(INTEL_PMC_IDX_FIXED_METRIC_BASE + 0)
>>>> +#define INTEL_PMC_IDX_TD_BAD_SPEC		(INTEL_PMC_IDX_FIXED_METRIC_BASE + 1)
>>>> +#define INTEL_PMC_IDX_TD_FE_BOUND		(INTEL_PMC_IDX_FIXED_METRIC_BASE + 2)
>>>> +#define INTEL_PMC_IDX_TD_BE_BOUND		(INTEL_PMC_IDX_FIXED_METRIC_BASE + 3)
>>>> +#define INTEL_PMC_MSK_ANY_SLOTS			((0xfull << INTEL_PMC_IDX_FIXED_METRIC_BASE) | \
>>>> +						 INTEL_PMC_MSK_FIXED_SLOTS)
>>>> +static inline bool is_metric_idx(int idx)
>>>> +{
>>>> +	return idx >= INTEL_PMC_IDX_FIXED_METRIC_BASE && idx <= INTEL_PMC_IDX_TD_BE_BOUND;
>>>> +}
>>>
>>> Something like:
>>>
>>> 	return (idx >> INTEL_PMC_IDX_FIXED_METRIC_BASE) & 0xf;
>>>
>>> might be faster code... (if it wasn't for 64bit literals being a pain,
>>> it could be a simple test instruction).
>>>
>>
>> is_metric_idx() is not a mask. It's to check if the idx between 49 and 52.
> 
> blergh, indeed. Check that it compiles into a single branch though, if
> it gets that wrong it needs hand holding.
> 
> One way would be to make these 48-51 and put BTS as 52, and then you do

Can we put BTS 47?
Now we only support L1 Topdown metrics. Probably there will be L2 
Topdown metrics. I think we need some space to extend.


Thanks,
Kan

> have a mask.
> 
> Another way would be to write it as:
> 
> 	(unsigned)(idx - INTEL_PMC_IDX_FIXED_METRIC_BASE) < 4;
> 
>