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Date: Sun, 12 Dec 2010 21:16:16 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: David Ahern <daahern@...co.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [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@...co.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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