Messages in this thread Patch in this message | | | From | kan.liang@linux ... | Subject | [PATCH V2] perf stat: Add hint for SMI cost measurement | Date | Fri, 26 Apr 2019 05:45:03 -0700 |
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From: Kan Liang <kan.liang@linux.intel.com>
Entering/exiting a C-state deeper than C0 may cause slight difference in counts between aperf and unhalted core cycles, which may impact the SMI cost.
Add smi_env_check() to check if C-state is completely disabled during the measurement. If not, give a hint to user.
Update the document as well.
Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Signed-off-by: Kan Liang <kan.liang@linux.intel.com> ---
Changes since V1: - Update changelog, document, and user-visible message
tools/perf/Documentation/perf-stat.txt | 5 +++++ tools/perf/builtin-stat.c | 25 +++++++++++++++++++++++++ 2 files changed, 30 insertions(+)
diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt index 39c05f8..19b7267 100644 --- a/tools/perf/Documentation/perf-stat.txt +++ b/tools/perf/Documentation/perf-stat.txt @@ -309,6 +309,11 @@ The output is SMI cycles%, equals to (aperf - unhalted core cycles) / aperf Users who wants to get the actual value can apply --no-metric-only. +Entering/exiting a C-state deeper than C0 may cause slight difference in counts +between aperf and unhalted core cycles, which may impact the SMI cost. +Please completely disable C-state during the measurement, +e.g. set idle=poll in grub. + EXAMPLES -------- diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c index c3625ec..e437788 100644 --- a/tools/perf/builtin-stat.c +++ b/tools/perf/builtin-stat.c @@ -87,6 +87,7 @@ #define DEFAULT_SEPARATOR " " #define FREEZE_ON_SMI_PATH "devices/cpu/freeze_on_smi" +#define CPUIDLE_CUR_DRV "devices/system/cpu/cpuidle/current_driver" static void print_counters(struct timespec *ts, int argc, const char **argv); @@ -1024,6 +1025,27 @@ __weak void arch_topdown_group_warn(void) { } +static void smi_env_check(void) +{ + char *name; + size_t len; + int err; + + err = sysfs__read_str(CPUIDLE_CUR_DRV, &name, &len); + if (err) { + pr_warning("Failed to read %s, err %d. Ignoring C-state status check.\n", + CPUIDLE_CUR_DRV, err); + return; + } + + if (strncmp(name, "none", 4)) { + pr_warning("Entering/exiting a C-state deeper than C0 may result inaccurate SMI cost.\n" + "Please completely disable C-state, e.g. set idle=poll in grub.\n"); + } + + free(name); +} + /* * Add default attributes, if there were no attributes specified or * if -d/--detailed, -d -d or -d -d -d is used: @@ -1196,6 +1218,9 @@ static int add_default_attributes(void) if (pmu_have_event("msr", "aperf") && pmu_have_event("msr", "smi")) { + + smi_env_check(); + if (!force_metric_only) stat_config.metric_only = true; err = parse_events(evsel_list, smi_cost_attrs, &errinfo); -- 2.7.4
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