linux-kernel - Re: [PATCH 04/13] perf/x86/amd: Support PERF_SAMPLE_WEIGHT using IBS OP

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Date:   Wed, 25 May 2022 15:58:15 +0300
From:   Stephane Eranian <eranian@...gle.com>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     peterz@...radead.org, acme@...nel.org, jolsa@...nel.org,
        namhyung@...nel.org, irogers@...gle.com, jmario@...hat.com,
        leo.yan@...aro.org, alisaidi@...zon.com, ak@...ux.intel.com,
        kan.liang@...ux.intel.com, dave.hansen@...ux.intel.com,
        hpa@...or.com, mingo@...hat.com, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, tglx@...utronix.de,
        bp@...en8.de, x86@...nel.org, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, sandipan.das@....com,
        ananth.narayan@....com, kim.phillips@....com,
        santosh.shukla@....com
Subject: Re: [PATCH 04/13] perf/x86/amd: Support PERF_SAMPLE_WEIGHT using IBS OP_DATA3[IbsDcMissLat]

On Wed, May 25, 2022 at 12:42 PM Ravi Bangoria <ravi.bangoria@....com> wrote:
>
> IBS Op data3 provides data cache miss latency which can be passed as
> sample->weight along with perf_mem_data_src. Note that sample->weight
> will be populated only when PERF_SAMPLE_DATA_SRC is also set, although
> both sample types are independent.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
> ---
>  arch/x86/events/amd/ibs.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
> index 6626caeed6a1..5a6e278713f4 100644
> --- a/arch/x86/events/amd/ibs.c
> +++ b/arch/x86/events/amd/ibs.c
> @@ -738,6 +738,12 @@ static void perf_ibs_get_mem_lvl(struct perf_event *event, u64 op_data2,
>                 return;
>         }
>
> +       /* Load latency (Data cache miss latency) */
> +       if (data_src->mem_op == PERF_MEM_OP_LOAD &&
> +           event->attr.sample_type & PERF_SAMPLE_WEIGHT) {
> +               data->weight.full = (op_data3 & IBS_DC_MISS_LAT_MASK) >> IBS_DC_MISS_LAT_SHIFT;
> +       }
> +
I think here you also need to handle the WEIGHT_STRUCT case and put
the cache miss latency in the right
field. This IBS field covers the cache line movement and not the whole
instruction latency which is the tag to ret field.
In the case of WEIGHT_STRUCT you need to fill out the two fields.

>         /* L2 Hit */
>         if ((op_data3 & IBS_L2_MISS_MASK) == 0) {
>                 /* Erratum #1293 */
> --
> 2.31.1
>