[PATCH 04/16] perf evsel: Disable branch flags/cycles for --callgraph lbr

Arnaldo Carvalho de Melo
2015-12-14T17:44:47Z

From: Andi Kleen <ak@linux.intel.com>

[The kernel patch needed for this is in tip now (b16a5b52eb9 perf/x86:
Add option to disable ...) So this user tools patch to make use of it
should be merged now]

Automatically disable collecting branch flags and cycles with
--call-graph lbr. This allows avoiding a bunch of extra MSR
reads in the PMI on Skylake.

When the kernel doesn't support the new flags they are automatically
cleared in the fallback code.

v2: Switch to use branch_sample_type instead of sample_type.
Adjust description.
Fix the fallback logic.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1449879144-29074-1-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/evsel.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 47f033089349..544e4400de13 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -36,6 +36,7 @@ static struct {
bool cloexec;
bool clockid;
bool clockid_wrong;
+ bool lbr_flags;
} perf_missing_features;

static clockid_t clockid;
@@ -574,7 +575,9 @@ perf_evsel__config_callgraph(struct perf_evsel *evsel,
} else {
perf_evsel__set_sample_bit(evsel, BRANCH_STACK);
attr->branch_sample_type = PERF_SAMPLE_BRANCH_USER |
- PERF_SAMPLE_BRANCH_CALL_STACK;
+ PERF_SAMPLE_BRANCH_CALL_STACK |
+ PERF_SAMPLE_BRANCH_NO_CYCLES |
+ PERF_SAMPLE_BRANCH_NO_FLAGS;
}
} else
pr_warning("Cannot use LBR callstack with branch stack. "
@@ -1337,6 +1340,9 @@ fallback_missing_features:
evsel->attr.mmap2 = 0;
if (perf_missing_features.exclude_guest)
evsel->attr.exclude_guest = evsel->attr.exclude_host = 0;
+ if (perf_missing_features.lbr_flags)
+ evsel->attr.branch_sample_type &= ~(PERF_SAMPLE_BRANCH_NO_FLAGS |
+ PERF_SAMPLE_BRANCH_NO_CYCLES);
retry_sample_id:
if (perf_missing_features.sample_id_all)
evsel->attr.sample_id_all = 0;
@@ -1455,6 +1461,12 @@ try_fallback:
} else if (!perf_missing_features.sample_id_all) {
perf_missing_features.sample_id_all = true;
goto retry_sample_id;
+ } else if (!perf_missing_features.lbr_flags &&
+ (evsel->attr.branch_sample_type &
+ (PERF_SAMPLE_BRANCH_NO_CYCLES |
+ PERF_SAMPLE_BRANCH_NO_FLAGS))) {
+ perf_missing_features.lbr_flags = true;
+ goto fallback_missing_features;
}

out_close:
--
2.1.0