linux-kernel - Re: [PATCH v1 1/5] perf cs-etm: Correct packets swapping in cs_etm_

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Date:   Fri, 16 Nov 2018 15:58:38 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Mike Leach <mike.leach@...aro.org>,
        Robert Walker <robert.walker@....com>,
        Al Grant <Al.Grant@....com>,
        Coresight ML <coresight@...ts.linaro.org>
Subject: Re: [PATCH v1 1/5] perf cs-etm: Correct packets swapping in
 cs_etm__flush()

On Sun, Nov 11, 2018 at 12:59:39PM +0800, Leo Yan wrote:
> The structure cs_etm_queue uses 'prev_packet' to point to previous
> packet, this can be used to combine with new coming packet to generate
> samples.
> 
> In function cs_etm__flush() it swaps packets only when the flag
> 'etm->synth_opts.last_branch' is true, this means that it will not
> swap packets if without option '--itrace=il' to generate last branch
> entries; thus for this case the 'prev_packet' doesn't point to the
> correct previous packet and the stale packet still will be used to
> generate sequential sample.  Thus if dump trace with 'perf script'
> command we can see the incorrect flow with the stale packet's address
> info.
> 
> This patch corrects packets swapping in cs_etm__flush(); except using
> the flag 'etm->synth_opts.last_branch' it also checks the another flag
> 'etm->sample_branches', if any flag is true then it swaps packets so
> can save correct content to 'prev_packet'.  Finally this can fix the
> wrong program flow dumping issue.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/util/cs-etm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 48ad217..fe18d7b 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -997,7 +997,7 @@ static int cs_etm__flush(struct cs_etm_queue *etmq)
>  	}
>  
>  swap_packet:
> -	if (etmq->etm->synth_opts.last_branch) {
> +	if (etm->sample_branches || etmq->etm->synth_opts.last_branch) {

This seems like the right thing to do, if only to be consistent with that is
done in cs_etm__sample().

Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>

>  		/*
>  		 * Swap PACKET with PREV_PACKET: PACKET becomes PREV_PACKET for
>  		 * the next incoming packet.
> -- 
> 2.7.4
>