linux-kernel - [PATCH V2 0/2] measure SMI cost (user)

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Date:   Fri, 26 May 2017 12:05:36 -0700
From:   kan.liang@...el.com
To:     acme@...nel.org, tglx@...utronix.de, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, eranian@...gle.com, jolsa@...nel.org,
        elliott@....com, ak@...ux.intel.com,
        Kan Liang <Kan.liang@...el.com>
Subject: [PATCH V2 0/2] measure SMI cost (user)

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 - unhalted core cycles).

A new sysfs entry /sys/device/cpu/freeze_on_smi is introduced to set
FREEZE_WHILE_SMM bit in IA32_DEBUGCTL. (kernel patch, which has been merged.
The commit ID is 6089327f5424f227bb6a8cf92363c2617e054453)

A new --smi-cost mode in perf stat is implemented to measure the SMI cost
by calculating unhalted core cycles and aperf results.

In practice, the percentages of SMI cycles is very useful for performance
oriented analysis. So the output will be SMI cycles% and SMI#.
For users who wants to get the actual value, they can apply --no-metric-only.

Here is an example of default output.

 Performance counter stats for 'sudo echo ':

SMI cycles%          SMI#
    0.1%              1

       0.010858678 seconds time elapsed

Changes since V1:
 - Check path array before trying to open that path. (Robert)
 - Refine change logs

Kan Liang (2):
  tools lib api fs: Add sysfs__write_int function
  perf stat: Add support to measure SMI cost

 tools/lib/api/fs/fs.c                  | 30 +++++++++++++++++++++
 tools/lib/api/fs/fs.h                  |  4 +++
 tools/perf/Documentation/perf-stat.txt | 14 ++++++++++
 tools/perf/builtin-stat.c              | 49 ++++++++++++++++++++++++++++++++++
 tools/perf/util/stat-shadow.c          | 33 +++++++++++++++++++++++
 tools/perf/util/stat.c                 |  2 ++
 tools/perf/util/stat.h                 |  2 ++
 7 files changed, 134 insertions(+)

-- 
2.7.4