linux-kernel - Re: [PATCH 11/21] perf/x86/intel/lbr: Support LBR

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Date:   Fri, 19 Jun 2020 15:15:09 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, acme@...nel.org, tglx@...utronix.de,
        bp@...en8.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, dave.hansen@...el.com,
        yu-cheng.yu@...el.com, bigeasy@...utronix.de, gorcunov@...il.com,
        hpa@...or.com, alexey.budankov@...ux.intel.com, eranian@...gle.com,
        ak@...ux.intel.com, like.xu@...ux.intel.com,
        yao.jin@...ux.intel.com
Subject: Re: [PATCH 11/21] perf/x86/intel/lbr: Support LBR_CTL



On 6/19/2020 2:40 PM, Peter Zijlstra wrote:
> On Fri, Jun 19, 2020 at 07:03:59AM -0700, kan.liang@...ux.intel.com wrote:
>> -	if (x86_pmu.extra_regs || x86_pmu.lbr_sel_map) {
>> +	if (x86_pmu.extra_regs || x86_pmu.lbr_sel_map || x86_pmu.lbr_ctl_map) {
> 
>> +	union {
>> +		u64		lbr_sel_mask;		   /* LBR_SELECT valid bits */
>> +		u64		lbr_ctl_mask;		   /* LBR_CTL valid bits */
>> +	};
> 
> This makes absolutely no sense. There is hoping the compiler realizes
> how stupid that is and fixes it for you, but shees.
> 

The lbr_ctl_map and the lbr_ctl_mask are two different things.

The lbr_ctl_map stores the mapping from PERF_SAMPLE_BRANCH_* to the 
corresponding filtering bits in LBR_CTL MSR. It is used to replace the 
old lbr_sel_map. The mapping information in the old lbr_sel_map is hard 
coded, and has a const type. But for arch LBR, the LBR filtering 
capabilities are enumerated from CPUID. We should not hard code the 
mapping. So I add a new variable lbr_ctl_map.

  	const int	*lbr_sel_map;		   /* lbr_select mappings */
+	int		*lbr_ctl_map;		   /* LBR_CTL mappings */


I think we cannot reuse the old lbr_sel_map for the lbr_ctl_map.

Thanks,
Kan

> Please, just keep the old name.
>