linux-kernel - Re: [PATCH] perf/x86/lbr: Simplify the exposure check for the LBR

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Message-ID: <5299a9a1-447e-be47-4b19-c5ada666b64e@linux.intel.com>
Date:   Thu, 18 Feb 2021 10:31:26 +0800
From:   Like Xu <like.xu@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kan Liang <kan.liang@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf/x86/lbr: Simplify the exposure check for the
 LBR_INFO registers

Hi Peter,

Would you help pick up this patch so that we can enable guest Arch LBR?

---
thx,likexu

On 2021/2/3 15:03, Like Xu wrote:
> If the platform supports LBR_INFO register, the x86_pmu.lbr_info will
> be assigned in intel_pmu_?_lbr_init_?() and it's safe to expose LBR_INFO
> in the x86_perf_get_lbr() directly, instead of relying on lbr_format check.
> 
> Also Architectural LBR has IA32_LBR_x_INFO instead of LBR_FORMAT_INFO_x
> to hold metadata for the operation, including mispredict, TSX, and
> elapsed cycle time information.
> 
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Signed-off-by: Like Xu <like.xu@...ux.intel.com>
> ---
>   arch/x86/events/intel/lbr.c | 4 +---
>   1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index 21890dacfcfe..355ea70f1879 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -1832,12 +1832,10 @@ void __init intel_pmu_arch_lbr_init(void)
>    */
>   int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
>   {
> -	int lbr_fmt = x86_pmu.intel_cap.lbr_format;
> -
>   	lbr->nr = x86_pmu.lbr_nr;
>   	lbr->from = x86_pmu.lbr_from;
>   	lbr->to = x86_pmu.lbr_to;
> -	lbr->info = (lbr_fmt == LBR_FORMAT_INFO) ? x86_pmu.lbr_info : 0;
> +	lbr->info = x86_pmu.lbr_info;
>   
>   	return 0;
>   }
>