Re: [PATCH v1 1/9] perf pmu: Add documentation

Ian Rogers
2022-11-14T17:04:23Z

On Mon, Nov 14, 2022 at 7:26 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
>
>
>
> On 2022-11-14 9:09 a.m., Ian Rogers wrote:
> > On Mon, Nov 14, 2022 at 5:40 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
> >>
> >>
> >>
> >> On 2022-11-14 2:51 a.m., Ian Rogers wrote:
> >>> Add documentation to struct perf_pmu and the associated structs of
> >>> perf_pmu_alias and perf_pmu_format.
> >>>
> >>> Signed-off-by: Ian Rogers <irogers@google.com>
> >>> ---
> >>> tools/perf/util/pmu.c | 14 ++++++
> >>> tools/perf/util/pmu.h | 105 +++++++++++++++++++++++++++++++++++++++---
> >>> 2 files changed, 113 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> >>> index 6a86e6af0903..a8f9f47c6ed9 100644
> >>> --- a/tools/perf/util/pmu.c
> >>> +++ b/tools/perf/util/pmu.c
> >>> @@ -31,10 +31,24 @@
> >>>
> >>> struct perf_pmu perf_pmu__fake;
> >>>
> >>> +/**
> >>> + * Values from a format file read from <sysfs>/devices/cpu/format/ held in
> >>> + * struct perf_pmu. For example, the contents of
> >>> + * <sysfs>/devices/cpu/format/event may be "config:0-7" and will be represented
> >>> + * here as name="event", value=PERF_PMU_FORMAT_VALUE_CONFIG and bits 0 to 7 will
> >>> + * be set.
> >>> + */
> >>> struct perf_pmu_format {
> >>> + /** The modifier/file name. */
> >>> char *name;
> >>> + /**
> >>> + * Which config value the format relates to. Supported values are from
> >>> + * PERF_PMU_FORMAT_VALUE_CONFIG to PERF_PMU_FORMAT_VALUE_CONFIG_END.
> >>> + */
> >>> int value;
> >>> + /** Which config bits are set by this format value. */
> >>> DECLARE_BITMAP(bits, PERF_PMU_FORMAT_BITS);
> >>> + /** Element on list within struct perf_pmu. */
> >>> struct list_head list;
> >>> };
> >>>
> >>> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
> >>> index 68e15c38ae71..29571c0f9d15 100644
> >>> --- a/tools/perf/util/pmu.h
> >>> +++ b/tools/perf/util/pmu.h
> >>> @@ -34,30 +34,91 @@ struct perf_pmu_caps {
> >>> };
> >>>
> >>> struct perf_pmu {
> >>> + /** The name of the PMU such as "cpu". */
> >>> char *name;
> >>> + /**
> >>> + * Optional alternate name for the PMU determined in architecture
> >>> + * specific code.
> >>> + */
> >>> char *alias_name;
> >>> + /**
> >>> + * Optional PMU identifier read from
> >>> + * <sysfs>/bus/event_source/devices/<name>/identifier.
> >>> + */
> >>> char *id;
> >>> + /**
> >>> + * Perf event attributed type value, read from
> >>> + * <sysfs>/bus/event_source/devices/<name>/type.
> >>> + */
> >>> __u32 type;
> >>> + /**
> >>> + * Can the PMU name be selected as if it were an event?
> >>> + */
> >>> bool selectable;
> >>> + /**
> >>> + * Is the PMU not within the CPU core? Determined by the presence of
> >>> + * <sysfs>/bus/event_source/devices/<name>/cpumask.
> >>> + */
> >>> bool is_uncore;
> >>> + /** Is the PMU name either cpu_core or cpu_atom. */
> >>
> >> I don't think we want to limit the hybrid names only to cpu_core or
> >> cpu_atom. Maybe something as below?
> >> /* Is a hybrid CPU PMU, e.g., cpu_core, cpu_atom. */
> >
> > Currently the hybrid code only works for cpu_core or cpu_atom, a
> > limitation of its implementation.
>
> I don't think so. See perf_pmu__hybrid_mounted(). If a PMU is named as
> "cpu_", we treat it as a hybrid CPU PMU. The cpu_core or cpu_atom should
> only be hard coded to specially handle some model-specific cases, e.g.,
> mem-loads-aux event.

Ugh.. Why is a property about something being a CPU named in an Intel
specific term for big little? Why wasn't this generalized? Why are CPU
PMUs assumed to be prefixed cpu_* .. ? The comment is factually
correct, we can hold off deprecating it on the assumption that it'd be
renamed to something more appropriate like is_cpu.

Thanks,
Ian

> Thanks,
> Kan
>
> > As pointed out in a later patch,
> > this bool isn't being used when it could be and I think we can work to
> > remove it. It would be possible to remove all uses of this with
> > perf_pmu__is_hybrid. As such I think it may be useful to mark the
> > hybrid variables in struct perf_pmu as deprecated while we work to
> > replace their use with more generic just any PMU code.
> >
> > Thanks,
> > Ian
> >
> >> Thanks,
> >> Kan
> >>
> >>> bool is_hybrid;
> >>> + /**
> >>> + * Are events auxiliary events? Determined in architecture specific
> >>> + * code.
> >>> + */
> >>> bool auxtrace;
> >>> + /**
> >>> + * Number of levels of :ppp precision supported by the PMU, read from
> >>> + * <sysfs>/bus/event_source/devices/<name>/caps/max_precise.
> >>> + */
> >>> int max_precise;
> >>> + /**
> >>> + * Optional default perf_event_attr determined in architecture specific
> >>> + * code.
> >>> + */
> >>> struct perf_event_attr *default_config;
> >>> + /**
> >>> + * Empty or the contents of either of:
> >>> + * <sysfs>/bus/event_source/devices/<name>/cpumask.
> >>> + * <sysfs>/bus/event_source/devices/<cpu>/cpus.
> >>> + */
> >>> struct perf_cpu_map *cpus;
> >>> - struct list_head format; /* HEAD struct perf_pmu_format -> list */
> >>> - struct list_head aliases; /* HEAD struct perf_pmu_alias -> list */
> >>> + /**
> >>> + * Holds the contents of files read from
> >>> + * <sysfs>/bus/event_source/devices/<name>/format/. The contents specify
> >>> + * which event parameter changes what config, config1 or config2 bits.
> >>> + */
> >>> + struct list_head format;
> >>> + /**
> >>> + * List of struct perf_pmu_alias. Each alias corresponds to an event
> >>> + * read from <sysfs>/bus/event_source/devices/<name>/events/ or from
> >>> + * json events in pmu-events.c.
> >>> + */
> >>> + struct list_head aliases;
> >>> + /** Has the list caps been initialized? */
> >>> bool caps_initialized;
> >>> + /** The length of the list caps. */
> >>> u32 nr_caps;
> >>> - struct list_head caps; /* HEAD struct perf_pmu_caps -> list */
> >>> - struct list_head list; /* ELEM */
> >>> + /**
> >>> + * Holds the contents of files read from
> >>> + * <sysfs>/bus/event_source/devices/<name>/caps/. The contents are pairs
> >>> + * of the filename with the value of its contents, for example,
> >>> + * max_precise (see above) may have a value of 3.
> >>> + */
> >>> + struct list_head caps;
> >>> + /** Element on pmus list in pmu.c. */
> >>> + struct list_head list;
> >>> + /** Element on perf_pmu__hybrid_pmus. */
> >>> struct list_head hybrid_list;
> >>>
> >>> + /** Features to inhibit when events on this PMU are opened. */
> >>> struct {
> >>> + /** Disables perf_event_attr exclude_guest and exclude_host. */
> >>> bool exclude_guest;
> >>> } missing_features;
> >>> };
> >>>
> >>> +/** A special global PMU used for testing. */
> >>> extern struct perf_pmu perf_pmu__fake;
> >>>
> >>> struct perf_pmu_info {
> >>> @@ -71,21 +132,53 @@ struct perf_pmu_info {
> >>>
> >>> #define UNIT_MAX_LEN 31 /* max length for event unit name */
> >>>
> >>> +/**
> >>> + * An event either read from sysfs or builtin in pmu-events.c, created by
> >>> + * parsing the pmu-events json files.
> >>> + */
> >>> struct perf_pmu_alias {
> >>> char *name;
> >>> + /** Optional short description of the event. */
> >>> char *desc;
> >>> + /** Optional long description. */
> >>> char *long_desc;
> >>> + /**
> >>> + * Optional topic such as cache or pipeline, particularly for json
> >>> + * events.
> >>> + */
> >>> char *topic;
> >>> + /** Comma separated parameter list. */
> >>> char *str;
> >>> - struct list_head terms; /* HEAD struct parse_events_term -> list */
> >>> - struct list_head list; /* ELEM */
> >>> + /** Owned list of the original parsed parameters. */
> >>> + struct list_head terms;
> >>> + /** List element of struct perf_pmu aliases. */
> >>> + struct list_head list;
> >>> + /** Units for the event, such as bytes or cache lines. */
> >>> char unit[UNIT_MAX_LEN+1];
> >>> + /** Value to scale read counter values by. */
> >>> double scale;
> >>> + /**
> >>> + * Does the file
> >>> + * <sysfs>/bus/event_source/devices/<pmu_name>/events/<name>.per-pkg or
> >>> + * equivalent json value exist and have the value 1.
> >>> + */
> >>> bool per_pkg;
> >>> + /**
> >>> + * Does the file
> >>> + * <sysfs>/bus/event_source/devices/<pmu_name>/events/<name>.snapshot
> >>> + * exist and have the value 1.
> >>> + */
> >>> bool snapshot;
> >>> + /** Is the event hidden and so not shown in perf list by default. */
> >>> bool deprecated;
> >>> + /**
> >>> + * A metric expression associated with an event. Doing this makes little
> >>> + * sense due to scale and unit applying to both.
> >>> + */
> >>> char *metric_expr;
> >>> + /** A name for the metric. unit applying to both. */
> >>> char *metric_name;
> >>> + /** The name copied from struct perf_pmu. */
> >>> char *pmu_name;
> >>> };
> >>>