Re: [PATCH] perf, record: Add clockid parameter

From: David Ahern
Date: Fri Mar 27 2015 - 13:11:11 EST


On 3/27/15 8:32 AM, Peter Zijlstra wrote:
On Fri, Mar 27, 2015 at 04:48:08AM -0700, tip-bot for Peter Zijlstra wrote:
perf: Add per event clockid support

And here the accompanying userspace; which I'd totally forgotten about.

XXX: do we want to store the clockid in the data file as well, such that
we can verify at perf-inject time the clocks match with our
expectations?

---
Subject: perf, record: Add clockid parameter

Teach perf-record about the new perf_event_attr::{use_clockid, clockid}
fields. Add a simple parameter to set the clock (if any) to be used for
the events to be recorded into the data file.

Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
tools/perf/builtin-record.c | 3 +++
tools/perf/perf.h | 1 +
tools/perf/util/evsel.c | 5 +++++
3 files changed, 9 insertions(+)

missing Documentation/perf-record.txt update


diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 18aad239b401..9d4ed884b1c8 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -739,6 +739,7 @@ static struct record record = {
.uses_mmap = true,
.default_per_cpu = true,
},
+ .clockid = -1,
},
.tool = {
.sample = process_sample_event,
@@ -842,6 +843,8 @@ struct option __record_options[] = {
"Sample machine registers on interrupt"),
OPT_BOOLEAN(0, "running-time", &record.opts.running_time,
"Record running/enabled time of read (:S) events"),
+ OPT_INTEGER('k', "clockid", &record.opts.clockid,
+ "clockid to use for events"),
OPT_END()
};

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index c38a085a5571..275c0c58fbbe 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -62,6 +62,7 @@ struct record_opts {
u64 user_interval;
bool sample_transaction;
unsigned initial_delay;
+ clockid_t clockid;
};

struct option;
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 358e5954baa8..309208b16632 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -761,6 +761,11 @@ void perf_evsel__config(struct perf_evsel *evsel, struct record_opts *opts)
attr->disabled = 0;
attr->enable_on_exec = 0;
}
+
+ if (opts->clockid >= 0) {
+ attr->use_clockid = 1;
+ attr->clockid = opts->clockid;
+ }
}

static int perf_evsel__alloc_fd(struct perf_evsel *evsel, int ncpus, int nthreads)


This is a new feature which means use_clockid on older kernels will fail. So need to catch that and throw an error -- perhaps yet another probe function.

Also, if the intent is to allow clock selection per event should there be an event modifier as well (see get_event_modifier())?

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