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    SubjectRe: [PATCH 1/2] perf tools: Add reference timestamp to perf header
    On Tue, Dec 07, 2010 at 06:54:44PM -0700, David Ahern wrote:
    > Add a reference timestamp to the perf header - snapshotting kernel
    > time to gettimeofday. This allows 'perf report' to convert kernel
    > timestamps to time-of-day which is convenient for comparing to other
    > (non perf related) log files.
    >
    > The timestamp is added using a feature bit for compatibility with
    > older binaries and data files.
    >
    > Signed-off-by: David Ahern <daahern@cisco.com>
    > ---
    > tools/perf/util/header.c | 51 +++++++++++++++++++++++++++++++++++++++++++++
    > tools/perf/util/header.h | 3 ++
    > tools/perf/util/session.c | 26 +++++++++++++++++++++++
    > 3 files changed, 80 insertions(+), 0 deletions(-)
    >
    > diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
    > index 76e949a..2fe893b 100644
    > --- a/tools/perf/util/header.c
    > +++ b/tools/perf/util/header.c
    > @@ -191,6 +191,40 @@ static int write_padded(int fd, const void *bf, size_t count,
    > return err;
    > }
    >
    > +static int perf_header__read_ref_time(struct perf_header *header,
    > + int fd, u64 offset, u64 size)
    > +{
    > + size_t sz_nsec = sizeof(header->nsec_ref);
    > + size_t sz_tv = sizeof(header->tv_ref);
    > + int err = -1;
    > +
    > + if (((size - offset) < (sz_nsec + sz_tv)) ||
    > + (read(fd, &header->nsec_ref, sz_nsec) != (ssize_t) sz_nsec) ||
    > + (read(fd, &header->tv_ref, sz_tv) != (ssize_t) sz_tv))
    > + goto out;

    Hmm, could we have endianness related troubles if we write the timespec on
    an arch and cross read from another, or other cross read issues?

    > +
    > + err = 0;
    > +
    > +out:
    > + return err;
    > +}
    > +
    > +static int perf_header__write_ref_time(struct perf_header *header, int fd)
    > +{
    > + size_t sz_nsec = sizeof(header->nsec_ref);
    > + size_t sz_tv = sizeof(header->tv_ref);
    > + int err = -1;
    > +
    > + if ((write(fd, &header->nsec_ref, sz_nsec) != (ssize_t) sz_nsec) ||
    > + (write(fd, &header->tv_ref, sz_tv) != (ssize_t) sz_tv))
    > + goto out;
    > +
    > + err = 0;
    > +
    > +out:
    > + return err;
    > +}
    > +
    > #define dsos__for_each_with_build_id(pos, head) \
    > list_for_each_entry(pos, head, node) \
    > if (!pos->has_build_id) \
    > @@ -483,6 +517,19 @@ static int perf_header__adds_write(struct perf_header *self, int fd)
    > perf_session__cache_build_ids(session);
    > }
    >
    > + if (perf_header__has_feat(self, HEADER_REFERENCE_TIME)) {
    > + struct perf_file_section *tref_sec;
    > +
    > + tref_sec = &feat_sec[idx++];
    > + tref_sec->offset = lseek(fd, 0, SEEK_CUR);
    > + err = perf_header__write_ref_time(self, fd);
    > + if (err < 0) {
    > + pr_debug("failed to write reference time\n");
    > + goto out_free;
    > + }
    > + tref_sec->size = lseek(fd, 0, SEEK_CUR) - tref_sec->offset;
    > + }
    > +
    > lseek(fd, sec_start, SEEK_SET);
    > err = do_write(fd, feat_sec, sec_size);
    > if (err < 0)
    > @@ -810,6 +857,10 @@ static int perf_file_section__process(struct perf_file_section *self,
    > if (perf_header__read_build_ids(ph, fd, self->offset, self->size))
    > pr_debug("Failed to read buildids, continuing...\n");
    > break;
    > + case HEADER_REFERENCE_TIME:
    > + if (perf_header__read_ref_time(ph, fd, self->offset, self->size))
    > + pr_debug("Failed to read reference time, continuing...\n");
    > + break;
    > default:
    > pr_debug("unknown feature %d, continuing...\n", feat);
    > }
    > diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
    > index 6335965..0721c78 100644
    > --- a/tools/perf/util/header.h
    > +++ b/tools/perf/util/header.h
    > @@ -19,6 +19,7 @@ struct perf_header_attr {
    > enum {
    > HEADER_TRACE_INFO = 1,
    > HEADER_BUILD_ID,
    > + HEADER_REFERENCE_TIME,
    > HEADER_LAST_FEATURE,
    > };
    >
    > @@ -59,6 +60,8 @@ struct perf_header {
    > u64 data_size;
    > u64 event_offset;
    > u64 event_size;
    > + u64 nsec_ref;
    > + struct timeval tv_ref;
    > DECLARE_BITMAP(adds_features, HEADER_FEAT_BITS);
    > };
    >
    > diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
    > index 3074d38..720838e 100644
    > --- a/tools/perf/util/session.c
    > +++ b/tools/perf/util/session.c
    > @@ -110,6 +110,29 @@ void perf_session__update_sample_type(struct perf_session *self)
    > perf_session__id_header_size(self);
    > }
    >
    > +static int perf_session__create_ref_time(struct perf_session *session)
    > +{
    > + struct timespec tp;
    > +
    > + /* race here between successive calls, but should be close enough */
    > + if (gettimeofday(&session->header.tv_ref, NULL) != 0) {
    > + pr_err("gettimeofday failed. Cannot set reference time.\n");
    > + return -1;
    > + }
    > +
    > + if (clock_gettime(CLOCK_MONOTONIC, &tp) != 0) {
    > + pr_err("clock_gettime failed. Cannot set reference time.\n");
    > + return -1;
    > + }
    > +
    > + session->header.nsec_ref = (u64) tp.tv_sec * NSEC_PER_SEC
    > + + (u64) tp.tv_nsec;
    > +
    > + perf_header__set_feat(&session->header, HEADER_REFERENCE_TIME);
    > +
    > + return 0;
    > +}
    > +
    > int perf_session__create_kernel_maps(struct perf_session *self)
    > {
    > int ret = machine__create_kernel_maps(&self->host_machine);
    > @@ -167,6 +190,9 @@ struct perf_session *perf_session__new(const char *filename, int mode, bool forc
    > */
    > if (perf_session__create_kernel_maps(self) < 0)
    > goto out_delete;
    > +
    > + if (perf_session__create_ref_time(self) < 0)
    > + goto out_delete;

    So, it does record it anytime?

    > }
    >
    > perf_session__update_sample_type(self);


    Other than that, looks good!


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