linux-kernel - Re: [PATCH 01/17] perf tools: Always force PERF_RECORD_FINISHED

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Date:	Fri, 13 Jun 2014 20:51:54 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jean Pihet <jean.pihet@...aro.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 01/17] perf tools: Always force
 PERF_RECORD_FINISHED_ROUND event

Hi Jiri,

2014-06-13 (금), 00:08 +0200, Jiri Olsa:
> The PERF_RECORD_FINISHED_ROUND governs queue flushing in
> reporting, so it needs to be stored for any kind of event.
> 
> Forcing the PERF_RECORD_FINISHED_ROUND event to be stored any
> time we finish the round and wrote at least one event.
> 
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
> Cc: David Ahern <dsahern@...il.com>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Jean Pihet <jean.pihet@...aro.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  tools/perf/builtin-record.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 378b85b..4869050 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -238,6 +238,7 @@ static struct perf_event_header finished_round_event = {
>  
>  static int record__mmap_read_all(struct record *rec)
>  {
> +	u64 bytes_written = rec->bytes_written;
>  	int i;
>  	int rc = 0;
>  
> @@ -250,7 +251,11 @@ static int record__mmap_read_all(struct record *rec)
>  		}
>  	}
>  
> -	if (perf_header__has_feat(&rec->session->header, HEADER_TRACING_DATA))
> +	/*
> +	 * Mark the round finished in case we wrote
> +	 * at least one event.
> +	 */
> +	if (bytes_written != rec->bytes_written)
>  		rc = record__write(rec, &finished_round_event, sizeof(finished_round_event));

Hmm.. what was the rational behind the original code?  Why did it flush
the events only if session has tracepoint events?  Frederic?

I guess this change alone can impact the performance in your case.
Jiri, do you have a test result of it?

Thanks,
Namhyung


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