On Tue, Mar 25, 2014 at 9:44 PM, Andi Kleen <[email protected]> wrote: > > From: Andi Kleen <[email protected]> > > [post with updated description] > > Time stamps are always implicitely enabled for record currently. > The old --time/-T option is a nop. > > The time stamps are needed to handle library mmaps correctly. > This mainly matters at program startup, but is not useful > when profiling long running programs. > > Allow the user to disable timestamps by using --no-time > > This can cause some minor misaccounting, but lowers the > size of the perf.data nicely: > > % perl -e 'while(1) {}' & > [1] 5827 > % perf record -p 5827 --no-time -c 1000003 sleep 1 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.089 MB perf.data (~3872 samples) ] > % perf record -p 5827 -c 1000003 sleep 1 > [ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.114 MB perf.data (~4967 samples) ] > > 22% smaller data file, even though we got more samples. > It also seems to speed up perf slightly, that is why we get more > samples. > But that measure of the number of samples is bogus most of the time. It is an estimate based on a standard sample size.
Timestamp are useful to order samples during reporting. How do you do with it if you monitor multi-threaded (multi-cpu) workloads. This is only good for single thread or single CPU measurements. Or am I missing something? > > The defaults are unchanged. > > Signed-off-by: Andi Kleen <[email protected]> > --- > tools/perf/builtin-record.c | 1 + > tools/perf/util/evsel.c | 9 ++++++--- > 2 files changed, 7 insertions(+), 3 deletions(-) > > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c > index 3c394bf..8e92d3c 100644 > --- a/tools/perf/builtin-record.c > +++ b/tools/perf/builtin-record.c > @@ -800,6 +800,7 @@ static const char * const record_usage[] = { > */ > static struct record record = { > .opts = { > + .sample_time = true, > .mmap_pages = UINT_MAX, > .user_freq = UINT_MAX, > .user_interval = ULLONG_MAX, > diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c > index 22e18a2..a15efc4 100644 > --- a/tools/perf/util/evsel.c > +++ b/tools/perf/util/evsel.c > @@ -613,9 +613,12 @@ void perf_evsel__config(struct perf_evsel *evsel, struct > record_opts *opts) > if (opts->period) > perf_evsel__set_sample_bit(evsel, PERIOD); > > - if (!perf_missing_features.sample_id_all && > - (opts->sample_time || !opts->no_inherit || > - target__has_cpu(&opts->target) || per_cpu)) > + /* > + * When the user explicitely disabled time don't force it here. > + */ > + if (opts->sample_time && > + (!perf_missing_features.sample_id_all && > + (!opts->no_inherit || target__has_cpu(&opts->target) || per_cpu))) > perf_evsel__set_sample_bit(evsel, TIME); > > if (opts->raw_samples) { > -- > 1.8.5.3 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
