linux-kernel - Re: [PATCH] perf vendor events: Fix DRAM_BW

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Date:   Thu, 22 Oct 2020 18:02:31 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Jin Yao <yao.jin@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <Linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>, "Jin, Yao" <yao.jin@...el.com>
Subject: Re: [PATCH] perf vendor events: Fix DRAM_BW_Use 0 issue for CLX/SKX

On Thu, Oct 22, 2020 at 5:54 PM Jin Yao <yao.jin@...ux.intel.com> wrote:
>
> Ian reports an issue that the metric DRAM_BW_Use often remains 0.
>
> The metric expression for DRAM_BW_Use on CLX/SKX:
>
> "( 64 * ( uncore_imc@..._count_read@ + uncore_imc@..._count_write@ ) / 1000000000 ) / duration_time"
>
> The counts of uncore_imc/cas_count_read/ and uncore_imc/cas_count_write/
> are scaled up by 64, that is to turn a count of cache lines into bytes,
> the count is then divided by 1000000000 to give GB.
>
> However, the counts of uncore_imc/cas_count_read/ and
> uncore_imc/cas_count_write/ have been scaled yet.
>
> The scale values are from sysfs, such as
> /sys/devices/uncore_imc_0/events/cas_count_read.scale.
> It's 6.103515625e-5 (64 / 1024.0 / 1024.0).
>
> So if we use original metric expression, the result is not correct.
>
> But the difficulty is, for SKL client, the counts are not scaled.
>
> The metric expression for DRAM_BW_Use on SKL:
>
> "64 * ( arb@...nt\\=0x81\\,umask\\=0x1@ + arb@...nt\\=0x84\\,umask\\=0x1@ ) / 1000000 / duration_time / 1000"
>
> root@...-ppc:~# perf stat -M DRAM_BW_Use -a -- sleep 1
>
>  Performance counter stats for 'system wide':
>
>                190      arb/event=0x84,umask=0x1/ #     1.86 DRAM_BW_Use
>         29,093,178      arb/event=0x81,umask=0x1/
>      1,000,703,287 ns   duration_time
>
>        1.000703287 seconds time elapsed
>
> The result is expected.
>
> So the easy way is just change the metric expression for CLX/SKX.
> This patch changes the metric expression to:
>
> "( ( ( uncore_imc@..._count_read@ + uncore_imc@..._count_write@ ) * 1048576 ) / 1000000000 ) / duration_time"
>
> 1048576 = 1024 * 1024.
>
> Before (tested on CLX):
>
> root@...-csl-2sp5 ~# perf stat -M DRAM_BW_Use -a -- sleep 1
>
>  Performance counter stats for 'system wide':
>
>             765.35 MiB  uncore_imc/cas_count_read/ #     0.00 DRAM_BW_Use
>               5.42 MiB  uncore_imc/cas_count_write/
>         1001515088 ns   duration_time
>
>        1.001515088 seconds time elapsed
>
> After:
>
> root@...-csl-2sp5 ~# perf stat -M DRAM_BW_Use -a -- sleep 1
>
>  Performance counter stats for 'system wide':
>
>             767.95 MiB  uncore_imc/cas_count_read/ #     0.80 DRAM_BW_Use

Nit, using ScaleUnit would allow this to be 0.80GB/s.

>               5.02 MiB  uncore_imc/cas_count_write/
>         1001900010 ns   duration_time
>
>        1.001900010 seconds time elapsed
>
> Fixes: 038d3b53c284 ("perf vendor events intel: Update CascadelakeX events to v1.08")
> Fixes: b5ff7f2799a4 ("perf vendor events: Update SkylakeX events to v1.21")
> Signed-off-by: Jin Yao <yao.jin@...ux.intel.com>

Acked-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json | 2 +-
>  tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json     | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json b/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json
> index de3193552277..00f4fcffa815 100644
> --- a/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json
> +++ b/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json
> @@ -329,7 +329,7 @@
>      },
>      {
>          "BriefDescription": "Average external Memory Bandwidth Use for reads and writes [GB / sec]",
> -        "MetricExpr": "( 64 * ( uncore_imc@..._count_read@ + uncore_imc@..._count_write@ ) / 1000000000 ) / duration_time",
> +        "MetricExpr": "( ( ( uncore_imc@..._count_read@ + uncore_imc@..._count_write@ ) * 1048576 ) / 1000000000 ) / duration_time",
>          "MetricGroup": "Memory_BW;SoC",
>          "MetricName": "DRAM_BW_Use"
>      },
> diff --git a/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json b/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json
> index f31794d3b926..0dd8b13b5cfb 100644
> --- a/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json
> +++ b/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json
> @@ -323,7 +323,7 @@
>      },
>      {
>          "BriefDescription": "Average external Memory Bandwidth Use for reads and writes [GB / sec]",
> -        "MetricExpr": "( 64 * ( uncore_imc@..._count_read@ + uncore_imc@..._count_write@ ) / 1000000000 ) / duration_time",
> +        "MetricExpr": "( ( ( uncore_imc@..._count_read@ + uncore_imc@..._count_write@ ) * 1048576 ) / 1000000000 ) / duration_time",
>          "MetricGroup": "Memory_BW;SoC",
>          "MetricName": "DRAM_BW_Use"
>      },
> --
> 2.17.1
>