Messages in this thread Patch in this message |  | | From | kan.liang@linux ... | Subject | [PATCH] perf stat: Add hint for SMI cost measurement | Date | Wed, 24 Apr 2019 08:46:32 -0700 |
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From: Kan Liang <kan.liang@linux.intel.com>
Cstate may cause drift between aperf and cycles, which impact the accuracy of SMI cost measurement.
Add smi_env_check() to check if cstate 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> --- tools/perf/Documentation/perf-stat.txt | 4 ++++ tools/perf/builtin-stat.c | 23 +++++++++++++++++++++++ 2 files changed, 27 insertions(+)
diff --git a/tools/perf/Documentation/perf-stat.txt b/tools/perf/Documentation/perf-stat.txt index 39c05f8..e0d8763 100644 --- a/tools/perf/Documentation/perf-stat.txt +++ b/tools/perf/Documentation/perf-stat.txt @@ -309,6 +309,10 @@ 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. +Cstate may cause drift between aperf and cycles. +Please completely disable cstate 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..ac273b4 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 +1025,25 @@ __weak void arch_topdown_group_warn(void) { } +static void smi_env_check(void) +{ + char *name; + size_t len; + + if (sysfs__read_str(CPUIDLE_CUR_DRV, &name, &len)) { + pr_warning("Failed to check cstate status.\n"); + return; + } + + if (strncmp(name, "none", 4)) { + pr_warning("Cstate may cause drift between aperf and cycles. " + "Please completely disable cstate, " + "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 +1216,9 @@ 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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