Re: [PATCH v6 1/6] perf header: Record first sample time and last sample time in perf file header

[Arnaldo Carvalho de Melo]

Em Mon, Nov 06, 2017 at 08:21:06PM +0800, Jin Yao escreveu:
> perf report/script/... have a --time option to limit the time range
> of output. That's very useful to slice large traces, e.g. when processing
> the output of perf script for some analysis.
> 
> But right now --time only supports absolute time. Also there is no fast
> way to get the start/end times of a given trace except for looking at it.
> This makes it hard to e.g. only decode the first half of the trace, which
> is useful for parallelization of scripts
> 
> Another problem is that perf records are variable size and there is no
> synchronization mechanism. So the only way to find the last sample reliably
> would be to walk all samples. But we want to avoid that in perf report/...
> because it is already quite expensive. That is why storing the first sample
> time and last sample time in perf record is better.
> 
> This patch creates a new header feature type HEADER_SAMPLE_TIME and related
> ops. Save the first sample time and the last sample time to the feature
> section in perf file header

I'll add a clarification here, right after your text:

". That will be done when, for instance, processing build-ids, where we
already have to process all samples to create the build-id table, take
advantage of that to further amortize that processing by storing
HEADER_SAMPLE_TIME to make 'perf report/script' faster when using
--time."

> 
> Change log:
> -----------
> v4: Use perf script time style for timestamp printing. Also add with
>     the printing of sample duration.
> 
> v3: Remove the definitions of first_sample_time/last_sample_time from
>     perf_session. Just define them in perf_evlist
> 
> Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
> ---
>  tools/perf/Documentation/perf.data-file-format.txt |  4 ++
>  tools/perf/util/evlist.h                           |  2 +
>  tools/perf/util/header.c                           | 60 ++++++++++++++++++++++
>  tools/perf/util/header.h                           |  1 +
>  4 files changed, 67 insertions(+)
> 
> diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
> index e90c59c..d5e3043 100644
> --- a/tools/perf/Documentation/perf.data-file-format.txt
> +++ b/tools/perf/Documentation/perf.data-file-format.txt
> @@ -238,6 +238,10 @@ struct auxtrace_index {
>  	struct auxtrace_index_entry entries[PERF_AUXTRACE_INDEX_ENTRY_COUNT];
>  };
>  
> +	HEADER_SAMPLE_TIME = 21,
> +
> +Two uint64_t for the time of first sample and the time of last sample.
> +
>  	other bits are reserved and should ignored for now
>  	HEADER_FEAT_BITS	= 256,
>  
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 8c433e9..a08f407 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -50,6 +50,8 @@ struct perf_evlist {
>  	struct perf_evsel *selected;
>  	struct events_stats stats;
>  	struct perf_env	*env;
> +	u64		first_sample_time;
> +	u64		last_sample_time;
>  };
>  
>  struct perf_evsel_str_handler {
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 6e59dcc..fd81c5b1 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -17,6 +17,7 @@
>  #include <sys/types.h>
>  #include <sys/utsname.h>
>  #include <unistd.h>
> +#include <linux/time64.h>
>  
>  #include "evlist.h"
>  #include "evsel.h"
> @@ -36,6 +37,7 @@
>  #include <api/fs/fs.h>
>  #include "asm/bug.h"
>  #include "tool.h"
> +#include "time-utils.h"
>  
>  #include "sane_ctype.h"
>  
> @@ -1181,6 +1183,20 @@ static int write_stat(struct feat_fd *ff __maybe_unused,
>  	return 0;
>  }
>  
> +static int write_sample_time(struct feat_fd *ff,
> +			     struct perf_evlist *evlist)
> +{
> +	int ret;
> +
> +	ret = do_write(ff, &evlist->first_sample_time,
> +		       sizeof(evlist->first_sample_time));
> +	if (ret < 0)
> +		return ret;
> +
> +	return do_write(ff, &evlist->last_sample_time,
> +			sizeof(evlist->last_sample_time));
> +}
> +
>  static void print_hostname(struct feat_fd *ff, FILE *fp)
>  {
>  	fprintf(fp, "# hostname : %s\n", ff->ph->env.hostname);
> @@ -1506,6 +1522,28 @@ static void print_group_desc(struct feat_fd *ff, FILE *fp)
>  	}
>  }
>  
> +static void print_sample_time(struct feat_fd *ff, FILE *fp)
> +{
> +	struct perf_session *session;
> +	char time_buf[32];
> +	double d;
> +
> +	session = container_of(ff->ph, struct perf_session, header);
> +
> +	timestamp__scnprintf_usec(session->evlist->first_sample_time,
> +				  time_buf, sizeof(time_buf));
> +	fprintf(fp, "# time of first sample : %s\n", time_buf);
> +
> +	timestamp__scnprintf_usec(session->evlist->last_sample_time,
> +				  time_buf, sizeof(time_buf));
> +	fprintf(fp, "# time of last sample : %s\n", time_buf);
> +
> +	d = (double)(session->evlist->last_sample_time -
> +		session->evlist->first_sample_time) / NSEC_PER_MSEC;
> +
> +	fprintf(fp, "# sample duration : %10.3f ms\n", d);
> +}
> +
>  static int __event_process_build_id(struct build_id_event *bev,
>  				    char *filename,
>  				    struct perf_session *session)
> @@ -2147,6 +2185,27 @@ static int process_cache(struct feat_fd *ff, void *data __maybe_unused)
>  	return -1;
>  }
>  
> +static int process_sample_time(struct feat_fd *ff, void *data __maybe_unused)
> +{
> +	struct perf_session *session;
> +	u64 first_sample_time, last_sample_time;
> +	int ret;
> +
> +	session = container_of(ff->ph, struct perf_session, header);
> +
> +	ret = do_read_u64(ff, &first_sample_time);
> +	if (ret)
> +		return -1;
> +
> +	ret = do_read_u64(ff, &last_sample_time);
> +	if (ret)
> +		return -1;
> +
> +	session->evlist->first_sample_time = first_sample_time;
> +	session->evlist->last_sample_time = last_sample_time;
> +	return 0;
> +}
> +
>  struct feature_ops {
>  	int (*write)(struct feat_fd *ff, struct perf_evlist *evlist);
>  	void (*print)(struct feat_fd *ff, FILE *fp);
> @@ -2204,6 +2263,7 @@ static const struct feature_ops feat_ops[HEADER_LAST_FEATURE] = {
>  	FEAT_OPN(AUXTRACE,	auxtrace,	false),
>  	FEAT_OPN(STAT,		stat,		false),
>  	FEAT_OPN(CACHE,		cache,		true),
> +	FEAT_OPR(SAMPLE_TIME,	sample_time,	false),
>  };
>  
>  struct header_print_data {
> diff --git a/tools/perf/util/header.h b/tools/perf/util/header.h
> index f7a16ee..1911831 100644
> --- a/tools/perf/util/header.h
> +++ b/tools/perf/util/header.h
> @@ -33,6 +33,7 @@ enum {
>  	HEADER_AUXTRACE,
>  	HEADER_STAT,
>  	HEADER_CACHE,
> +	HEADER_SAMPLE_TIME,
>  	HEADER_LAST_FEATURE,
>  	HEADER_FEAT_BITS	= 256,
>  };
> -- 
> 2.7.4