Re: [PATCH v2 01/17] perf tools: Configure contextID tracing in CPU-wide mode

[Suzuki K Poulose]

Hi Mathieu,

On 24/05/2019 18:34, Mathieu Poirier wrote:
> When operating in CPU-wide mode being notified of contextID changes is
> required so that the decoding mechanic is aware of the process context
> switch.
>
> Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>


> Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>

I am sorry but, I don't remember reviewing this patch in the previous
postings. But here we go.

> ---
>   tools/perf/arch/arm/util/cs-etm.c | 126 +++++++++++++++++++++++++-----
>   tools/perf/util/cs-etm.h          |  12 +++
>   2 files changed, 119 insertions(+), 19 deletions(-)
>
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index 911426721170..3912f0bf04ed 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -35,8 +35,100 @@ struct cs_etm_recording {
>   	size_t			snapshot_size;
>   };
>   


>   static bool cs_etm_is_etmv4(struct auxtrace_record *itr, int cpu);
>   
> +static int cs_etm_set_context_id(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 TRCIRD2 */
> +	snprintf(path, PATH_MAX, "cpu%d/%s",
> +		 cpu, metadata_etmv4_ro[CS_ETMV4_TRCIDR2]);
> +	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;
> +	}
> +
> +	/*
> +	 * TRCIDR2.CIDSIZE, bit [9-5], indicates whether contextID tracing
> +	 * is supported:
> +	 *  0b00000 Context ID tracing is not supported.
> +	 *  0b00100 Maximum of 32-bit Context ID size.
> +	 *  All other values are reserved.
> +	 */
> +	val = BMVAL(val, 5, 9);
> +	if (!val || val != 0x4) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +
> +	/* All good, let the kernel know */
> +	evsel->attr.config |= (1 << ETM_OPT_CTXTID);
> +	err = 0;
> +
> +out:
> +
> +	return err;
> +}
> +
> +static int cs_etm_set_option(struct auxtrace_record *itr,
> +			     struct perf_evsel *evsel, u32 option)
> +{
> +	int i, err = -EINVAL;
> +	struct cpu_map *event_cpus = evsel->evlist->cpus;
> +	struct cpu_map *online_cpus = cpu_map__new(NULL);
> +
> +	/* Set option of each CPU we have */
> +	for (i = 0; i < cpu__max_cpu(); i++) {
> +		if (!cpu_map__has(event_cpus, i) ||
> +		    !cpu_map__has(online_cpus, i))
> +			continue;
> +
> +		switch (option) {
> +		case ETM_OPT_CTXTID:
> +			err = cs_etm_set_context_id(itr, evsel, i);
> +			if (err)
> +				goto out;
> +			break;
> +		default:
> +			goto out;
> +		}
> +	}

I am not too familiar with the perf tool code. But, isn't there a way
to force the config bit, right from the beginning when the events are
created, when we know that we are doing a CPU wide tracing, along with
the other config bits ?



> +	err = 0;
> +out:
> +	cpu_map__put(online_cpus);
> +	return err;
> +}
> +
>   static int cs_etm_parse_snapshot_options(struct auxtrace_record *itr,
>   					 struct record_opts *opts,
>   					 const char *str)
> @@ -105,8 +197,9 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
>   				container_of(itr, struct cs_etm_recording, itr);
>   	struct perf_pmu *cs_etm_pmu = ptr->cs_etm_pmu;
>   	struct perf_evsel *evsel, *cs_etm_evsel = NULL;
> -	const struct cpu_map *cpus = evlist->cpus;
> +	struct cpu_map *cpus = evlist->cpus;
>   	bool privileged = (geteuid() == 0 || perf_event_paranoid() < 0);
> +	int err = 0;
>   
>   	ptr->evlist = evlist;
>   	ptr->snapshot_mode = opts->auxtrace_snapshot_mode;
> @@ -241,19 +334,24 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
>   
>   	/*
>   	 * In the case of per-cpu mmaps, we need the CPU on the
> -	 * AUX event.
> +	 * AUX event.  We also need the contextID in order to be notified
> +	 * when a context switch happened.
>   	 */
> -	if (!cpu_map__empty(cpus))
> +	if (!cpu_map__empty(cpus)) {
>   		perf_evsel__set_sample_bit(cs_etm_evsel, CPU);
>   
> +		err = cs_etm_set_option(itr, cs_etm_evsel, ETM_OPT_CTXTID);
> +		if (err)
> +			goto out;
> +	}
> +
>   	/* Add dummy event to keep tracking */
>   	if (opts->full_auxtrace) {
>   		struct perf_evsel *tracking_evsel;
> -		int err;
>   
>   		err = parse_events(evlist, "dummy:u", NULL);
>   		if (err)
> -			return err;
> +			goto out;
>   
>   		tracking_evsel = perf_evlist__last(evlist);
>   		perf_evlist__set_tracking_event(evlist, tracking_evsel);
> @@ -266,7 +364,8 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
>   			perf_evsel__set_sample_bit(tracking_evsel, TIME);
>   	}
>   
> -	return 0;
> +out:
> +	return err;
>   }


> diff --git a/tools/perf/util/cs-etm.h b/tools/perf/util/cs-etm.h
> index 0e97c196147a..826c9eedaf5c 100644
> --- a/tools/perf/util/cs-etm.h
> +++ b/tools/perf/util/cs-etm.h
> @@ -103,6 +103,18 @@ struct intlist *traceid_list;
>   #define KiB(x) ((x) * 1024)
>   #define MiB(x) ((x) * 1024 * 1024)
>   
> +/*
> + * Create a contiguous bitmask starting at bit position @l and ending at
> + * position @h. For example
> + * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
> + *
> + * Carbon copy of implementation found in $KERNEL/include/linux/bitops.h
> + */
> +#define GENMASK(h, l) \
> +	(((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
> +

minor nit: Could this be placed in a more generic header file for the other
parts of the perf tool to consume ?

> +#define BMVAL(val, lsb, msb)	((val & GENMASK(msb, lsb)) >> lsb)
> +


Cheers
Suzuki