From: Kan Liang <kan.li...@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 <a...@redhat.com>
Signed-off-by: Kan Liang <kan.li...@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
