linux-kernel - Re: [PATCH v2 02/17] perf tools: Configure timestsamp generation in CPU-wide mode

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Date:   Fri, 7 Jun 2019 10:41:48 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     mathieu.poirier@...aro.org, acme@...nel.org
Cc:     peterz@...radead.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, leo.yan@...aro.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        coresight@...ts.linaro.org
Subject: Re: [PATCH v2 02/17] perf tools: Configure timestsamp generation in
 CPU-wide mode



On 24/05/2019 18:34, Mathieu Poirier wrote:
> When operating in CPU-wide mode tracers need to generate timestamps in
> order to correlate the code being traced on one CPU with what is executed
> on other CPUs.
> 
> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> ---
>   tools/perf/arch/arm/util/cs-etm.c | 57 +++++++++++++++++++++++++++++++
>   1 file changed, 57 insertions(+)
> 
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index 3912f0bf04ed..be1e4f20affa 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -99,6 +99,54 @@ static int cs_etm_set_context_id(struct auxtrace_record *itr,
>   	return err;
>   }
>   
> +static int cs_etm_set_timestamp(struct auxtrace_record *itr,
> +				struct perf_evsel *evsel, int cpu)
> +{
> +	struct cs_etm_recording *ptr;
> +	struct perf_pmu *cs_etm_pmu;
> +	char path[PATH_MAX];
> +	int err = -EINVAL;
> +	u32 val;
> +
> +	ptr = container_of(itr, struct cs_etm_recording, itr);
> +	cs_etm_pmu = ptr->cs_etm_pmu;
> +
> +	if (!cs_etm_is_etmv4(itr, cpu))
> +		goto out;
> +
> +	/* Get a handle on TRCIRD0 */
> +	snprintf(path, PATH_MAX, "cpu%d/%s",
> +		 cpu, metadata_etmv4_ro[CS_ETMV4_TRCIDR0]);
> +	err = perf_pmu__scan_file(cs_etm_pmu, path, "%x", &val);
> +
> +	/* There was a problem reading the file, bailing out */
> +	if (err != 1) {
> +		pr_err("%s: can't read file %s\n",
> +		       CORESIGHT_ETM_PMU_NAME, path);
> +		goto out;
> +	}
> +
> +	/*
> +	 * TRCIDR0.TSSIZE, bit [28-24], indicates whether global timestamping
> +	 * is supported:
> +	 *  0b00000 Global timestamping is not implemented
> +	 *  0b00110 Implementation supports a maximum timestamp of 48bits.
> +	 *  0b01000 Implementation supports a maximum timestamp of 64bits.
> +	 */
> +	val &= GENMASK(28, 24);
> +	if (!val) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> +	/* All good, let the kernel know */
> +	evsel->attr.config |= (1 << ETM_OPT_TS);
> +	err = 0;
> +
> +out:
> +	return err;
> +}
> +
>   static int cs_etm_set_option(struct auxtrace_record *itr,
>   			     struct perf_evsel *evsel, u32 option)
>   {
> @@ -118,6 +166,11 @@ static int cs_etm_set_option(struct auxtrace_record *itr,
>   			if (err)
>   				goto out;
>   			break;
> +		case ETM_OPT_TS:
> +			err = cs_etm_set_timestamp(itr, evsel, i);
> +			if (err)
> +				goto out;
> +			break;
>   		default:
>   			goto out;
>   		}
> @@ -343,6 +396,10 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
>   		err = cs_etm_set_option(itr, cs_etm_evsel, ETM_OPT_CTXTID);
>   		if (err)
>   			goto out;
> +
> +		err = cs_etm_set_option(itr, cs_etm_evsel, ETM_OPT_TS);
> +		if (err)
> +			goto out;

nit: Could we not do this in one shot, say :

	cs_etm_set_option(itr, cs_etm_evsel, ETM_OPT_TS | ETM_OPT_CTXTID) ?

rather than iterating over the per-CPU events twice ? The cs_etm_set_option()
could simply replace the switch() to :

	if (option & ETM_OPT_1)
		do_something_for_1()
	if (option & ETM_OPT_2)
		do_something_for_2();
	if (option & ~(ETM_OPT_1 | ETM_OPT_2 |...))
		/* do unsupported option */


Cheers
Suzuki