linux-kernel - Re: [PATCH 0/3]measure SMI cost

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Date:   Fri, 31 Mar 2017 14:51:15 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     "Liang, Kan" <kan.liang@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...nel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [PATCH 0/3]measure SMI cost

On Thu, Mar 23, 2017 at 11:25 AM,  <kan.liang@...el.com> wrote:
> From: Kan Liang <Kan.liang@...el.com>
>
> Currently, there is no way to measure the time cost in System management
> mode (SMM) by perf.
>
> Intel perfmon supports FREEZE_WHILE_SMM bit in IA32_DEBUGCTL. Once it sets,
> the PMU core counters will freeze on SMI handler. But it will not have an
> effect on free running counters. E.g. APERF counter.
> The cost of SMI can be measured by (aperf - cycles).
>
> A new sysfs entry /sys/device/cpu/freeze_on_smi is introduced to set
> FREEZE_WHILE_SMM bit in IA32_DEBUGCTL.
>
> A new --smi-cost mode in perf stat is implemented to measure the SMI cost
> by calculating cycles and aperf results. In practice, the percentages of
> SMI cycles should be more useful than absolute value. So the output will be
> the percentage of SMI cycles and SMI#.
>
You are talking about the percentage of what cycles?
Wallclock, unhalted_ref_cycles, unhalted_core_cycles?
I
> Here is an example output.
>
>  Performance counter stats for 'sudo echo ':
>
> SMI cycles%          SMI#
>     0.1%              1
>
>        0.010858678 seconds time elapsed
>
>
> Kan Liang (3):
>   perf/x86: add sysfs entry to freeze counter on SMI
>   tools lib api fs: Add sysfs__write_int function
>   perf stat: Add support to measure SMI cost
>
>  arch/x86/events/core.c                 | 10 +++++++
>  arch/x86/events/intel/core.c           | 48 ++++++++++++++++++++++++++++++++++
>  arch/x86/events/perf_event.h           |  3 +++
>  arch/x86/include/asm/msr-index.h       |  1 +
>  tools/lib/api/fs/fs.c                  | 29 ++++++++++++++++++++
>  tools/lib/api/fs/fs.h                  |  4 +++
>  tools/perf/Documentation/perf-stat.txt |  9 +++++++
>  tools/perf/builtin-stat.c              | 48 ++++++++++++++++++++++++++++++++++
>  tools/perf/util/stat-shadow.c          | 33 +++++++++++++++++++++++
>  tools/perf/util/stat.c                 |  2 ++
>  tools/perf/util/stat.h                 |  2 ++
>  11 files changed, 189 insertions(+)
>
> --
> 2.7.4
>