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Message-ID: <8bd875a5-6540-4137-ae7a-22ec516c4716@linaro.org>
Date: Mon, 10 Mar 2025 10:04:08 +0000
From: James Clark <james.clark@...aro.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
Robin Murphy <robin.murphy@....com>, Leo Yan <leo.yan@....com>,
linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] perf list: Collapse similar events across PMUs
On 07/03/2025 5:35 pm, Ian Rogers wrote:
> On Fri, Mar 7, 2025 at 6:08 AM James Clark <james.clark@...aro.org> wrote:
>>
>>
>>
>> On 05/03/2025 9:40 pm, Ian Rogers wrote:
>>> On Tue, Mar 4, 2025 at 5:50 AM James Clark <james.clark@...aro.org> wrote:
>>>>
>>>> Instead of showing multiple line items with the same event name and
>>>> description, show a single line and concatenate all PMUs that this
>>>> event can belong to.
>>>>
>>>> Don't do it for json output. Machine readable output doesn't need to be
>>>> minimized, and changing the "Unit" field to a list type would break
>>>> backwards compatibility.
>>>>
>>>> Before:
>>>> $ perf list -v
>>>> ...
>>>> br_indirect_spec
>>>> [Branch speculatively executed,indirect branch. Unit: armv8_cortex_a53]
>>>> br_indirect_spec
>>>> [Branch speculatively executed,indirect branch. Unit: armv8_cortex_a57]
>>>>
>>>> After:
>>>>
>>>> $ perf list -v
>>>> ...
>>>> br_indirect_spec
>>>> [Branch speculatively executed,indirect branch. Unit: armv8_cortex_a53,armv8_cortex_a57]
>>>>
>>>> Signed-off-by: James Clark <james.clark@...aro.org>
>>>> ---
>>>> tools/perf/builtin-list.c | 2 ++
>>>> tools/perf/util/pmus.c | 75 +++++++++++++++++++++++++++++++++++++-----
>>>> tools/perf/util/print-events.h | 1 +
>>>> 3 files changed, 70 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/tools/perf/builtin-list.c b/tools/perf/builtin-list.c
>>>> index fed482adb039..aacd7beae2a0 100644
>>>> --- a/tools/perf/builtin-list.c
>>>> +++ b/tools/perf/builtin-list.c
>>>> @@ -516,6 +516,7 @@ int cmd_list(int argc, const char **argv)
>>>> .print_event = default_print_event,
>>>> .print_metric = default_print_metric,
>>>> .skip_duplicate_pmus = default_skip_duplicate_pmus,
>>>> + .collapse_events = true
>>>
>>> So collapse_events is put in the callbacks but isn't a callback. I
>>> think skipping duplicates and collapsing are the same thing, I'd
>>> prefer it if there weren't two terms for the same thing. If you prefer
>>> collapsing as a name then default_skip_duplicate_pmus can be
>>> default_collapse_pmus.
>>>
>>
>> I can use the existing callback and rename it. That does have the effect
>> of disabling this behavior in verbose mode which may be useful or may be
>> unexpected to some people. But it seems pretty 50/50 so fewer callbacks
>> are probably better.
>>
>>>> };
>>>> const char *cputype = NULL;
>>>> const char *unit_name = NULL;
>>>> @@ -574,6 +575,7 @@ int cmd_list(int argc, const char **argv)
>>>> .print_event = json_print_event,
>>>> .print_metric = json_print_metric,
>>>> .skip_duplicate_pmus = json_skip_duplicate_pmus,
>>>> + .collapse_events = false
>>>> };
>>>> ps = &json_ps;
>>>> } else {
>>>> diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
>>>> index 4d60bac2d2b9..cb1b14ade25b 100644
>>>> --- a/tools/perf/util/pmus.c
>>>> +++ b/tools/perf/util/pmus.c
>>>> @@ -453,17 +453,50 @@ static int cmp_sevent(const void *a, const void *b)
>>>> /* Order by PMU name. */
>>>> if (as->pmu == bs->pmu)
>>>> return 0;
>>>> - return strcmp(as->pmu_name ?: "", bs->pmu_name ?: "");
>>>> + ret = strcmp(as->pmu_name ?: "", bs->pmu_name ?: "");
>>>> + if (ret)
>>>> + return ret;
>>>> +
>>>> + /* Order by remaining displayed fields for purposes of deduplication later */
>>>> + ret = strcmp(as->scale_unit ?: "", bs->scale_unit ?: "");
>>>> + if (ret)
>>>> + return ret;
>>>> + ret = !!as->deprecated - !!bs->deprecated;
>>>> + if (ret)
>>>> + return ret;
>>>> + ret = strcmp(as->desc ?: "", bs->desc ?: "");
>>>> + if (ret)
>>>> + return ret;
>>>> + return strcmp(as->long_desc ?: "", bs->long_desc ?: "");
>>>> }
>>>>
>>>> -static bool pmu_alias_is_duplicate(struct sevent *a, struct sevent *b)
>>>> +enum dup_type {
>>>> + UNIQUE,
>>>> + DUPLICATE,
>>>> + SAME_TEXT
>>>> +};
>>>> +
>>>> +static enum dup_type pmu_alias_duplicate_type(struct sevent *a, struct sevent *b)
>>>> {
>>>> /* Different names -> never duplicates */
>>>> if (strcmp(a->name ?: "//", b->name ?: "//"))
>>>> - return false;
>>>> + return UNIQUE;
>>>> +
>>>> + /* Duplicate PMU name and event name -> hide completely */
>>>> + if (strcmp(a->pmu_name, b->pmu_name) == 0)
>>>> + return DUPLICATE;
>>>> +
>>>> + /* Any other different display text -> not duplicate */
>>>> + if (strcmp(a->topic ?: "", b->topic ?: "") ||
>>>> + strcmp(a->scale_unit ?: "", b->scale_unit ?: "") ||
>>>> + a->deprecated != b->deprecated ||
>>>> + strcmp(a->desc ?: "", b->desc ?: "") ||
>>>> + strcmp(a->long_desc ?: "", b->long_desc ?: "")) {
>>>> + return UNIQUE;
>>>> + }
>>>>
>>>> - /* Don't remove duplicates for different PMUs */
>>>> - return strcmp(a->pmu_name, b->pmu_name) == 0;
>>>> + /* Same display text but different PMU -> collapse */
>>>> + return SAME_TEXT;
>>>> }
>>>>
>>>> struct events_callback_state {
>>>> @@ -501,6 +534,21 @@ static int perf_pmus__print_pmu_events__callback(void *vstate,
>>>> return 0;
>>>> }
>>>>
>>>> +static void concat_pmu_names(char *pmu_names, size_t size, const char *a, const char *b)
>>>> +{
>>>> + size_t len = strlen(pmu_names);
>>>> + size_t added;
>>>> +
>>>> + if (len)
>>>> + added = snprintf(pmu_names + len, size - len, ",%s", b);
>>>> + else
>>>> + added = snprintf(pmu_names, size, "%s,%s", a, b);
>>>> +
>>>> + /* Truncate with ... */
>>>> + if (added > 0 && added + len >= size)
>>>> + sprintf(pmu_names + size - 4, "...");
>>>> +}
>>>> +
>>>> void perf_pmus__print_pmu_events(const struct print_callbacks *print_cb, void *print_state)
>>>> {
>>>> struct perf_pmu *pmu;
>>>> @@ -510,6 +558,7 @@ void perf_pmus__print_pmu_events(const struct print_callbacks *print_cb, void *p
>>>> struct events_callback_state state;
>>>> bool skip_duplicate_pmus = print_cb->skip_duplicate_pmus(print_state);
>>>> struct perf_pmu *(*scan_fn)(struct perf_pmu *);
>>>> + char pmu_names[128] = {0};
>>>>
>>>> if (skip_duplicate_pmus)
>>>> scan_fn = perf_pmus__scan_skip_duplicates;
>>>> @@ -539,12 +588,21 @@ void perf_pmus__print_pmu_events(const struct print_callbacks *print_cb, void *p
>>>> qsort(aliases, len, sizeof(struct sevent), cmp_sevent);
>>>> for (int j = 0; j < len; j++) {
>>>> /* Skip duplicates */
>>>> - if (j < len - 1 && pmu_alias_is_duplicate(&aliases[j], &aliases[j + 1]))
>>>> - goto free;
>>>> + if (j < len - 1) {
>>>> + enum dup_type dt = pmu_alias_duplicate_type(&aliases[j], &aliases[j + 1]);
>>>> +
>>>> + if (dt == DUPLICATE) {
>>>> + goto free;
>>>> + } else if (print_cb->collapse_events && dt == SAME_TEXT) {
>>>> + concat_pmu_names(pmu_names, sizeof(pmu_names),
>>>> + aliases[j].pmu_name, aliases[j+1].pmu_name);
>>>> + goto free;
>>>> + }
>>>> + }
>>>
>>> I think a label called 'free' is a little unfortunate given the
>>> function called free.
>>> When I did things with sevent I was bringing over previous `perf list`
>>> code mainly so that the perf list output before and after the changes
>>> was identical. I wonder if this logic would be better placed in the
>>> callback like default_print_event which already maintains state
>>> (last_topic) to optionally print different things. This may better
>>> encapsulate the behavior rather than the logic being in the PMU code.
>>>
>>
>> Yeah I can have a look at putting it in one of the callbacks. But in the
>> end builtin-list.c is the only user of perf_pmus__print_pmu_events()
>> anyway so makes you wonder if the whole thing can be moved to
>> builtin-list and open coded without the callbackyness.
>
> I wanted to hide some of the innards of pmus, so I think that's the
> reason it is as it is. The whole `sevent` was pre-existing and
> maintained so that the output was the same.
>
>>>>
>>>> print_cb->print_event(print_state,
>>>> aliases[j].topic,
>>>> - aliases[j].pmu_name,
>>>> + pmu_names[0] ? pmu_names : aliases[j].pmu_name,
>>>> aliases[j].name,
>>>> aliases[j].alias,
>>>> aliases[j].scale_unit,
>>>> @@ -553,6 +611,7 @@ void perf_pmus__print_pmu_events(const struct print_callbacks *print_cb, void *p
>>>> aliases[j].desc,
>>>> aliases[j].long_desc,
>>>> aliases[j].encoding_desc);
>>>
>>> The encoding_desc will have a PMU with the suffix removed as per
>>> skipping duplicates:
>>> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmu.c?h=perf-tools-next#n1954
>>> So I think something like:
>>> ```
>>> br_mis_pred_retired
>>> [Instruction architecturally executed,mispredicted branch. Unit:
>>> armv9_cortex_a510,armv9_cortex_a710]
>>> ```
>>> Would have an encoding of `armv9_cortex_a510/.../` without the a710
>>> encoding being present. That said, I'm not sure anyone cares :-)
>>>
>>> Thanks,
>>> Ian
>>>
>>
>> Ah, in that case I'll disable it for --detailed as well as --json. I
>> could compare encoding_desc in pmu_alias_duplicate_type() but they'll
>> always be different because of the PMU name, so there's no point. And
>> displaying multiple encoding_descs would be fiddly too.
>
> So I'd like not to have the encoding_desc removed. It is useful for
> debugging.. I meant by people not caring that the format of that
> string is under specified, so the PMU name not being 100% accurate
> likely doesn't affect people.
>
> Thanks,
> Ian
>
>
By 'disabled' I meant disable this collapsing of PMU names, so with
--detailed you'll get the existing full list of events with their
encoding_descs, no change there. Sorry for the confusion.
>>>> + pmu_names[0] = '\0';
>>>> free:
>>>> zfree(&aliases[j].name);
>>>> zfree(&aliases[j].alias);
>>>> diff --git a/tools/perf/util/print-events.h b/tools/perf/util/print-events.h
>>>> index 445efa1636c1..e91f9f830a2a 100644
>>>> --- a/tools/perf/util/print-events.h
>>>> +++ b/tools/perf/util/print-events.h
>>>> @@ -27,6 +27,7 @@ struct print_callbacks {
>>>> const char *threshold,
>>>> const char *unit);
>>>> bool (*skip_duplicate_pmus)(void *print_state);
>>>> + bool collapse_events;
>>>> };
>>>>
>>>> /** Print all events, the default when no options are specified. */
>>>>
>>>> --
>>>> 2.34.1
>>>>
>>
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