On Fri, Jul 31, 2020 at 06:52:36PM +0300, Alexey Budankov wrote:
>
> On 31.07.2020 0:39, Jiri Olsa wrote:
> > Adding new CLOCK_DATA feature that stores reference times
> > when -k/--clockid option is specified.
> >
> > It contains clock id and its reference time together with
> > wall clock time taken at the 'same time', both values are
> > in nanoseconds.
> >
> > The format of data is as below:
> >
> > struct {
> > u32 version; /* version = 1 */
> > u32 clockid;
> > u64 clockid_time_ns;
> > u64 wall_clock_ns;
> > };
> >
> > This clock reference times will be used in following changes
> > to display wall clock for perf events.
> >
> > It's available only for recording with clockid specified,
> > because it's the only case where we can get reference time
> > to wallclock time. It's can't do that with perf clock yet.
> >
> > Original-patch-by: David Ahern <dsah...@gmail.com>
> > Signed-off-by: Jiri Olsa <jo...@kernel.org>
> > ---
> > .../Documentation/perf.data-file-format.txt | 13 ++
> > tools/perf/builtin-record.c | 41 +++++++
> > tools/perf/util/env.h | 12 ++
> > tools/perf/util/header.c | 112 ++++++++++++++++++
> > tools/perf/util/header.h | 1 +
> > 5 files changed, 179 insertions(+)
> >
> > diff --git a/tools/perf/Documentation/perf.data-file-format.txt
> > b/tools/perf/Documentation/perf.data-file-format.txt
> > index b6472e463284..c484e81987c7 100644
> > --- a/tools/perf/Documentation/perf.data-file-format.txt
> > +++ b/tools/perf/Documentation/perf.data-file-format.txt
> > @@ -389,6 +389,19 @@ struct {
> > Example:
> > cpu pmu capabilities: branches=32, max_precise=3, pmu_name=icelake
> >
> > + HEADER_CLOCK_DATA = 29,
> > +
> > + Contains clock id and its reference time together with wall clock
> > + time taken at the 'same time', both values are in nanoseconds.
> > + The format of data is as below.
> > +
> > +struct {
> > + u32 version; /* version = 1 */
> > + u32 clockid;
> > + u64 clockid_time_ns;
> > + u64 wall_clock_ns;
> > +};
> > +
> > other bits are reserved and should ignored for now
> > HEADER_FEAT_BITS = 256,
> >
> > diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> > index 468c669519a6..f8280e721e1a 100644
> > --- a/tools/perf/builtin-record.c
> > +++ b/tools/perf/builtin-record.c
> > @@ -70,6 +70,7 @@
> > #include <linux/time64.h>
> > #include <linux/zalloc.h>
> > #include <linux/bitmap.h>
> > +#include <sys/time.h>
> >
> > struct switch_output {
> > bool enabled;
> > @@ -1203,6 +1204,9 @@ static void record__init_features(struct record *rec)
> > if (!(rec->opts.use_clockid && rec->opts.clockid_res_ns))
> > perf_header__clear_feat(&session->header, HEADER_CLOCKID);
> >
> > + if (!rec->opts.use_clockid)
> > + perf_header__clear_feat(&session->header, HEADER_CLOCK_DATA);
> > +
> > perf_header__clear_feat(&session->header, HEADER_DIR_FORMAT);
> > if (!record__comp_enabled(rec))
> > perf_header__clear_feat(&session->header, HEADER_COMPRESSED);
> > @@ -1551,6 +1555,40 @@ static int record__setup_sb_evlist(struct record
> > *rec)
> > return 0;
> > }
> >
> > +static int record__init_clock(struct record *rec)
> > +{
> > + struct perf_session *session = rec->session;
> > + struct timespec ref_clockid;
> > + struct timeval ref_tod;
> > + u64 ref;
> > +
> > + if (!rec->opts.use_clockid)
> > + return 0;
> > +
> > + session->header.env.clock.clockid = rec->opts.clockid;
> > +
> > + if (gettimeofday(&ref_tod, NULL) != 0) {
> > + pr_err("gettimeofday failed, cannot set reference time.\n");
> > + return -1;
> > + }
> > +
> > + if (clock_gettime(rec->opts.clockid, &ref_clockid)) {
> > + pr_err("clock_gettime failed, cannot set reference time.\n");
> > + return -1;
> > + }
>
> It might also want to be implemented in a loop and iteration with minimal
> time delta is chosen to improve synchronization accuracy and also mitigate
> possible context switches between gettimeofday() and clock_gettime() calls.
right, we could make this more accurate.. I'll post some follow up
change with that
thanks,
jirka
