linux-kernel - Re: [PATCH 2/2] perf cs-etm: Set time on synthesised samples to preserve ordering

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Date:   Thu, 15 Apr 2021 13:54:16 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     coresight@...ts.linaro.org, al.grant@....com,
        branislav.rankov@....com, denik@...omium.org,
        suzuki.poulose@....com, Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] perf cs-etm: Set time on synthesised samples to
 preserve ordering

On Wed, Apr 14, 2021 at 05:39:19PM +0300, James Clark wrote:
> The following attribute is set when synthesising samples in
> timed decoding mode:
> 
>     attr.sample_type |= PERF_SAMPLE_TIME;
> 
> This results in new samples that appear to have timestamps but
> because we don't assign any timestamps to the samples, when the
> resulting inject file is opened again, the synthesised samples
> will be on the wrong side of the MMAP or COMM events.
>

I understand the problem.  Once again an issue caused by CS and the kernel
having a different view of time. 

> For example this results in the samples being associated with
> the perf binary, rather than the target of the record:
> 
>     perf record -e cs_etm/@..._etr0/u top
>     perf inject -i perf.data -o perf.inject --itrace=i100il
>     perf report -i perf.inject
> 
> Where 'Command' == perf should show as 'top':
> 
>     # Overhead  Command  Source Shared Object  Source Symbol           Target Symbol           Basic Block Cycles
>     # ........  .......  ....................  ......................  ......................  ..................
>     #
>         31.08%  perf     [unknown]             [.] 0x000000000040c3f8  [.] 0x000000000040c3e8  -
> 
> If the perf.data file is opened directly with perf, without the
> inject step, then this already works correctly because the
> events are synthesised after the COMM and MMAP events and
> no second sorting happens. Re-sorting only happens when opening
> the perf.inject file for the second time so timestamps are
> needed.
> 
> Using the timestamp from the AUX record mirrors the current
> behaviour when opening directly with perf, because the events
> are generated on the call to cs_etm__process_queues().
> 
> Signed-off-by: James Clark <james.clark@....com>
> Co-developed-by: Al Grant <al.grant@....com>
> Signed-off-by: Al Grant <al.grant@....com>

Suzuki is correct, your name has to appear after Al's.

> ---
>  tools/perf/util/cs-etm.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index c25da2ffa8f3..d0fa9dce47f1 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -54,6 +54,7 @@ struct cs_etm_auxtrace {
>  	u8 sample_instructions;
>  
>  	int num_cpu;
> +	u64 latest_kernel_timestamp;
>  	u32 auxtrace_type;
>  	u64 branches_sample_type;
>  	u64 branches_id;
> @@ -1192,6 +1193,8 @@ static int cs_etm__synth_instruction_sample(struct cs_etm_queue *etmq,
>  	event->sample.header.misc = cs_etm__cpu_mode(etmq, addr);
>  	event->sample.header.size = sizeof(struct perf_event_header);
>  
> +	if (!etm->timeless_decoding)
> +		sample.time = etm->latest_kernel_timestamp;
>  	sample.ip = addr;
>  	sample.pid = tidq->pid;
>  	sample.tid = tidq->tid;
> @@ -1248,6 +1251,8 @@ static int cs_etm__synth_branch_sample(struct cs_etm_queue *etmq,
>  	event->sample.header.misc = cs_etm__cpu_mode(etmq, ip);
>  	event->sample.header.size = sizeof(struct perf_event_header);
>  
> +	if (!etm->timeless_decoding)
> +		sample.time = etm->latest_kernel_timestamp;
>  	sample.ip = ip;
>  	sample.pid = tidq->pid;
>  	sample.tid = tidq->tid;
> @@ -2412,9 +2417,10 @@ static int cs_etm__process_event(struct perf_session *session,
>  	else if (event->header.type == PERF_RECORD_SWITCH_CPU_WIDE)
>  		return cs_etm__process_switch_cpu_wide(etm, event);
>  
> -	if (!etm->timeless_decoding &&
> -	    event->header.type == PERF_RECORD_AUX)
> +	if (!etm->timeless_decoding && event->header.type == PERF_RECORD_AUX) {
> +		etm->latest_kernel_timestamp = sample_kernel_timestamp;

It will be fun to fix this when 8.4 comes out but for now it's the best we've
got.

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

>  		return cs_etm__process_queues(etm);
> +	}
>  
>  	return 0;
>  }
> -- 
> 2.28.0
>