linux-kernel - Re: [PATCH] perf/x86/intel: Define bit macros for FixCntrCtl MSR

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Date:   Thu, 30 Mar 2023 10:46:01 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhang Tinghao <tinghao.zhang@...el.com>,
        Zhuocheng Ding <zhuocheng.ding@...el.com>
Subject: Re: [PATCH] perf/x86/intel: Define bit macros for FixCntrCtl MSR



On 2023-03-30 9:07 a.m., Peter Zijlstra wrote:
> On Thu, Mar 30, 2023 at 09:28:46AM +0800, Dapeng Mi wrote:
>> Define bit macros for FixCntrCtl MSR and replace the bit hardcoding
>> with these bit macros. This would make code be more human-readable.
>>
>> Perf commands 'perf stat -e "instructions,cycles,ref-cycles"' and
>> 'perf record -e "instructions,cycles,ref-cycles"' pass.
>>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
>> ---
>>  arch/x86/events/intel/core.c      | 18 +++++++++---------
>>  arch/x86/include/asm/perf_event.h | 10 ++++++++++
>>  2 files changed, 19 insertions(+), 9 deletions(-)
>>
>> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
>> index 070cc4ef2672..b7c0bb78ed59 100644
>> --- a/arch/x86/events/intel/core.c
>> +++ b/arch/x86/events/intel/core.c
>> @@ -2451,7 +2451,7 @@ static void intel_pmu_disable_fixed(struct perf_event *event)
>>  
>>  	intel_clear_masks(event, idx);
>>  
>> -	mask = 0xfULL << ((idx - INTEL_PMC_IDX_FIXED) * 4);
>> +	mask = intel_fixed_bits(idx - INTEL_PMC_IDX_FIXED, INTEL_FIXED_BITS_MASK);
>>  	cpuc->fixed_ctrl_val &= ~mask;
> 
> So maybe it's me, but I find the original far easier to read :/ That new
> things I need to look up every single identifier before I can tell wth
> it does.

The intel_fixed_bits() tries to replace the duplicate "bit << (idx *
4);". I think it should be a good improvement. Maybe we should rename it
to intel_shift_fixed_bits_by_idx(). Is it better?

If not, I think at least we should use some macros to replace the magic
number.

Thanks,
Kan