linux-kernel - Re: [PATCH 2/6] perf cs-etm: Split setup and timestamp search functions

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Date:   Mon, 19 Jul 2021 13:38:21 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     James Clark <james.clark@....com>
Cc:     acme@...nel.org, coresight@...ts.linaro.org, leo.yan@...aro.org,
        al.grant@....com, branislav.rankov@....com, suzuki.poulose@....com,
        anshuman.khandual@....com, Mike Leach <mike.leach@...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 2/6] perf cs-etm: Split setup and timestamp search
 functions

On Tue, Jul 13, 2021 at 04:40:04PM +0100, James Clark wrote:
> This refactoring has some benefits:
>  * Decoding is done to find the timestamp. If we want to print errors
>    when maps aren't available, then doing it from cs_etm__setup_queue()
>    may cause warnings to be printed.
>  * The cs_etm__setup_queue() flow is shared between timed and timeless
>    modes, so it needs to be guarded by an if statement which can now
>    be removed.
>  * Allows moving the setup queues function earlier.
>  * If data was piped in, then not all queues would be filled so it
>    wouldn't have worked properly anyway. Now it waits for flush so
>    data in all queues will be available.
> 
> The motivation for this is to decouple setup functions with ones that
> involve decoding. That way we can move the setup function earlier when
> the formatted/unformatted trace information is available.
> 
> Signed-off-by: James Clark <james.clark@....com>
> ---
>  tools/perf/util/cs-etm.c | 41 ++++++++++++++++++++++++++++------------
>  1 file changed, 29 insertions(+), 12 deletions(-)

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

> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 4c69ef391f60..426e99c07ca9 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -809,29 +809,32 @@ static int cs_etm__setup_queue(struct cs_etm_auxtrace *etm,
>  			       struct auxtrace_queue *queue,
>  			       unsigned int queue_nr)
>  {
> -	int ret = 0;
> -	unsigned int cs_queue_nr;
> -	u8 trace_chan_id;
> -	u64 cs_timestamp;
>  	struct cs_etm_queue *etmq = queue->priv;
>  
>  	if (list_empty(&queue->head) || etmq)
> -		goto out;
> +		return 0;
>  
>  	etmq = cs_etm__alloc_queue(etm);
>  
> -	if (!etmq) {
> -		ret = -ENOMEM;
> -		goto out;
> -	}
> +	if (!etmq)
> +		return -ENOMEM;
>  
>  	queue->priv = etmq;
>  	etmq->etm = etm;
>  	etmq->queue_nr = queue_nr;
>  	etmq->offset = 0;
>  
> -	if (etm->timeless_decoding)
> -		goto out;
> +	return 0;
> +}
> +
> +static int cs_etm__queue_first_cs_timestamp(struct cs_etm_auxtrace *etm,
> +					    struct cs_etm_queue *etmq,
> +					    unsigned int queue_nr)
> +{
> +	int ret = 0;
> +	unsigned int cs_queue_nr;
> +	u8 trace_chan_id;
> +	u64 cs_timestamp;
>  
>  	/*
>  	 * We are under a CPU-wide trace scenario.  As such we need to know
> @@ -2218,13 +2221,27 @@ static int cs_etm__process_timeless_queues(struct cs_etm_auxtrace *etm,
>  static int cs_etm__process_queues(struct cs_etm_auxtrace *etm)
>  {
>  	int ret = 0;
> -	unsigned int cs_queue_nr, queue_nr;
> +	unsigned int cs_queue_nr, queue_nr, i;
>  	u8 trace_chan_id;
>  	u64 cs_timestamp;
>  	struct auxtrace_queue *queue;
>  	struct cs_etm_queue *etmq;
>  	struct cs_etm_traceid_queue *tidq;
>  
> +	/*
> +	 * Pre-populate the heap with one entry from each queue so that we can
> +	 * start processing in time order across all queues.
> +	 */
> +	for (i = 0; i < etm->queues.nr_queues; i++) {
> +		etmq = etm->queues.queue_array[i].priv;
> +		if (!etmq)
> +			continue;
> +
> +		ret = cs_etm__queue_first_cs_timestamp(etm, etmq, i);
> +		if (ret)
> +			return ret;
> +	}
> +
>  	while (1) {
>  		if (!etm->heap.heap_cnt)
>  			goto out;
> -- 
> 2.28.0
>