Re: [Patch v5 1/6] perf x86/topdown: Complete topdown slots/metrics events check

From: Mi, Dapeng
Date: Wed Oct 09 2024 - 05:57:10 EST


On 10/8/2024 1:55 PM, Ian Rogers wrote:
> On Thu, Sep 12, 2024 at 10:21 PM Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx> wrote:
>> It's not complete to check whether an event is a topdown slots or
>> topdown metrics event by only comparing the event name since user
>> may assign the event by RAW format, e.g.
>>
>> perf stat -e '{instructions,cpu/r400/,cpu/r8300/}' sleep 1
>>
>> Performance counter stats for 'sleep 1':
>>
>> <not counted> instructions
>> <not counted> cpu/r400/
>> <not supported> cpu/r8300/
>>
>> 1.002917796 seconds time elapsed
>>
>> 0.002955000 seconds user
>> 0.000000000 seconds sys
>>
>> The RAW format slots and topdown-be-bound events are not recognized and
>> not regroup the events, and eventually cause error.
>>
>> Thus add two helpers arch_is_topdown_slots()/arch_is_topdown_metrics()
>> to detect whether an event is topdown slots/metrics event by comparing
>> the event config directly, and use these two helpers to replace the
>> original event name comparisons.
>>
>> Reviewed-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>> Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>
>> ---
>> tools/perf/arch/x86/util/evlist.c | 8 ++---
>> tools/perf/arch/x86/util/evsel.c | 3 +-
>> tools/perf/arch/x86/util/topdown.c | 48 +++++++++++++++++++++++++++++-
>> tools/perf/arch/x86/util/topdown.h | 2 ++
>> 4 files changed, 55 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/perf/arch/x86/util/evlist.c b/tools/perf/arch/x86/util/evlist.c
>> index cebdd483149e..79799865a62a 100644
>> --- a/tools/perf/arch/x86/util/evlist.c
>> +++ b/tools/perf/arch/x86/util/evlist.c
>> @@ -78,14 +78,14 @@ int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs)
>> if (topdown_sys_has_perf_metrics() &&
>> (arch_evsel__must_be_in_group(lhs) || arch_evsel__must_be_in_group(rhs))) {
>> /* Ensure the topdown slots comes first. */
>> - if (strcasestr(lhs->name, "slots") && !strcasestr(lhs->name, "uops_retired.slots"))
>> + if (arch_is_topdown_slots(lhs))
>> return -1;
>> - if (strcasestr(rhs->name, "slots") && !strcasestr(rhs->name, "uops_retired.slots"))
>> + if (arch_is_topdown_slots(rhs))
>> return 1;
>> /* Followed by topdown events. */
>> - if (strcasestr(lhs->name, "topdown") && !strcasestr(rhs->name, "topdown"))
>> + if (arch_is_topdown_metrics(lhs) && !arch_is_topdown_metrics(rhs))
>> return -1;
>> - if (!strcasestr(lhs->name, "topdown") && strcasestr(rhs->name, "topdown"))
>> + if (!arch_is_topdown_metrics(lhs) && arch_is_topdown_metrics(rhs))
>> return 1;
>> }
>>
>> diff --git a/tools/perf/arch/x86/util/evsel.c b/tools/perf/arch/x86/util/evsel.c
>> index 090d0f371891..181f2ba0bb2a 100644
>> --- a/tools/perf/arch/x86/util/evsel.c
>> +++ b/tools/perf/arch/x86/util/evsel.c
>> @@ -6,6 +6,7 @@
>> #include "util/pmu.h"
>> #include "util/pmus.h"
>> #include "linux/string.h"
>> +#include "topdown.h"
>> #include "evsel.h"
>> #include "util/debug.h"
>> #include "env.h"
>> @@ -44,7 +45,7 @@ bool arch_evsel__must_be_in_group(const struct evsel *evsel)
>> strcasestr(evsel->name, "uops_retired.slots"))
>> return false;
>>
>> - return strcasestr(evsel->name, "topdown") || strcasestr(evsel->name, "slots");
>> + return arch_is_topdown_metrics(evsel) || arch_is_topdown_slots(evsel);
>> }
>>
>> int arch_evsel__hw_name(struct evsel *evsel, char *bf, size_t size)
>> diff --git a/tools/perf/arch/x86/util/topdown.c b/tools/perf/arch/x86/util/topdown.c
>> index 3f9a267d4501..49f25d67ed77 100644
>> --- a/tools/perf/arch/x86/util/topdown.c
>> +++ b/tools/perf/arch/x86/util/topdown.c
>> @@ -32,6 +32,52 @@ bool topdown_sys_has_perf_metrics(void)
>> }
>>
>> #define TOPDOWN_SLOTS 0x0400
>> +bool arch_is_topdown_slots(const struct evsel *evsel)
>> +{
> Perhaps: assert(evsel__find_pmu(evsel)->is_core);

assert? we don't need an assert as this helper just detects if a evsel is
slots event and it's reasonable if the evsel is not. But it's nice to add
the is_core check. Thanks.


>
>> + if (evsel->core.attr.config == TOPDOWN_SLOTS)
>> + return true;
>> +
>> + return false;
>> +}
>> +
>> +static int compare_topdown_event(void *vstate, struct pmu_event_info *info)
>> +{
>> + int *config = vstate;
>> + int event = 0;
>> + int umask = 0;
>> + char *str;
>> +
>> + if (!strcasestr(info->name, "topdown"))
>> + return 0;
>> +
>> + str = strcasestr(info->str, "event=");
>> + if (str)
>> + sscanf(str, "event=%x", &event);
>> +
>> + str = strcasestr(info->str, "umask=");
>> + if (str)
>> + sscanf(str, "umask=%x", &umask);
>> +
>> + if (event == 0 && *config == (event | umask << 8))
>> + return 1;
>> +
>> + return 0;
>> +}
>> +
>> +bool arch_is_topdown_metrics(const struct evsel *evsel)
>> +{
>> + struct perf_pmu *pmu = evsel__find_pmu(evsel);
>> + int config = evsel->core.attr.config;
>> +
>> + if (!pmu || !pmu->is_core)
>> + return false;
>> +
>> + if (perf_pmu__for_each_event(pmu, false, &config,
>> + compare_topdown_event))
>> + return true;
>> +
>> + return false;
>> +}
>
> Doing a linear search over every event is painful perf_pmu__have_event
> will try to binary search. The search rejects all events without
> "topdown" in their name, it then sees if the event code is 0 and the
> event|umask match the sysfs/json event. Is there ever a case the
> "topdown" string isn't at the beginning of the string? If it is it

Currently all topdown events would start with "topdown" prefix.


> should be possible to binary search to the start of the topdown
> events.
>
> Strictly you shouldn't hard code the config positions of event and
> umask, they are in the format list:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmu.h?h=perf-tools-next#n113
> There is code doing similar to this here:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmu.c?h=perf-tools-next#n2285
> but it avoids the scanf, uses formats...
> It seems reasonable this code should reject all non-zero configs
> before searching all core PMU events. It could also use
> perf_pmu__name_from_config. So:
> ```
> bool evsel__is_topdown_metric_event(const struct evsel *evsel)
> {
> struct perf_pmu *pmu;
> const char *name_from_config;
>
> if (evsel->core.attr.config & 0xFF != 0) /* All topdown events have
> an event code of 0. */
> return false;
>
> pmu = evsel__find_pmu(evsel);
> if (!pmu || !pmu->is_core)
> return false;
>
> name_from_config = perf_pmu__name_from_config(pmu, config);
> return name_from_config && !strcasestr(name_from_config, "topdown);
> }
> ```

Good point! would cook a patch to implement this. Thanks.


> We could tweak perf_pmu__name_from_config to be pased a "filter". In
> this case the filter would skip events without topdown in their name,
> without doing a config comparison.
>
> If later we change perf_pmu__name_from_config to say sort events in a
> list by config, then this code could take advantage of that. Perhaps
> for now there should just be an optional "prefix" that can be used to
> binary search to the events.
> ```
> name_from_config = perf_pmu__name_from_config(pmu, config,
> /*prefix=*/"topdown");
> ```
>
> Thanks,
> Ian
>
>> /*
>> * Check whether a topdown group supports sample-read.
>> @@ -44,7 +90,7 @@ bool arch_topdown_sample_read(struct evsel *leader)
>> if (!evsel__sys_has_perf_metrics(leader))
>> return false;
>>
>> - if (leader->core.attr.config == TOPDOWN_SLOTS)
>> + if (arch_is_topdown_slots(leader))
>> return true;
>>
>> return false;
>> diff --git a/tools/perf/arch/x86/util/topdown.h b/tools/perf/arch/x86/util/topdown.h
>> index 46bf9273e572..1bae9b1822d7 100644
>> --- a/tools/perf/arch/x86/util/topdown.h
>> +++ b/tools/perf/arch/x86/util/topdown.h
>> @@ -3,5 +3,7 @@
>> #define _TOPDOWN_H 1
>>
>> bool topdown_sys_has_perf_metrics(void);
>> +bool arch_is_topdown_slots(const struct evsel *evsel);
>> +bool arch_is_topdown_metrics(const struct evsel *evsel);
>>
>> #endif
>> --
>> 2.40.1
>>