Re: [PATCH v3 05/12] perf evsel: Add a helper to get the value of a config field

[James Clark <james.clark@linaro.org>]

On 16/12/2025 22:44, Ian Rogers wrote:
> On Fri, Dec 12, 2025 at 7:32 AM James Clark <james.clark@linaro.org> wrote:
>>
>> This will be used by aux PMUs to read an already written value for
>> configuring their events and for also testing.
>>
>> Its helper pmu_format_unpack() does the opposite of the existing
>> pmu_format_value() so rename that one to pmu_format_pack() so it's clear
>> how they are related.
>>
>> Signed-off-by: James Clark <james.clark@linaro.org>
>> ---
>>   tools/perf/util/evsel.h |  2 ++
>>   tools/perf/util/pmu.c   | 77 ++++++++++++++++++++++++++++++++++++++++++-------
>>   2 files changed, 68 insertions(+), 11 deletions(-)
>>
>> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
>> index a08130ff2e47a887b19f6c47bfa9f51e0c40d226..092904a61ec7afdc59253f9b78a9fe8b7cb5bfa7 100644
>> --- a/tools/perf/util/evsel.h
>> +++ b/tools/perf/util/evsel.h
>> @@ -575,6 +575,8 @@ void evsel__uniquify_counter(struct evsel *counter);
>>          ((((src) >> (pos)) & ((1ull << (size)) - 1)) << (63 - ((pos) + (size) - 1)))
>>
>>   u64 evsel__bitfield_swap_branch_flags(u64 value);
>> +int evsel__get_config_val(struct perf_pmu *pmu, struct evsel *evsel,
>> +                         const char *config_name, u64 *val);
>>   void evsel__set_config_if_unset(struct perf_pmu *pmu, struct evsel *evsel,
>>                                  const char *config_name, u64 val);
>>
>> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
>> index 514cba91f5d99b399d2d6a1e350971660c54a9fc..ef7358ad1fb955f29f2e68b3d0ce711754e4d67c 100644
>> --- a/tools/perf/util/pmu.c
>> +++ b/tools/perf/util/pmu.c
>> @@ -144,8 +144,8 @@ struct perf_pmu_format {
>>   };
>>
>>   static int pmu_aliases_parse(struct perf_pmu *pmu);
>> -static void pmu_format_value(unsigned long *format, __u64 value, __u64 *v,
>> -                            bool zero);
>> +static void pmu_format_pack(unsigned long *format, __u64 value, __u64 *v,
>> +                           bool zero);
>>   static struct perf_pmu_format *pmu_find_format(const struct list_head *formats,
>>                                                 const char *name);
>>
>> @@ -1377,6 +1377,61 @@ bool evsel__is_aux_event(const struct evsel *evsel)
>>          return pmu && pmu->auxtrace;
>>   }
>>
>> +/*
>> + * Unpacks a raw config[n] value using the sparse bitfield that defines a
>> + * format attr. For example "config1:1,6-7,44" defines a 4 bit value across non
>> + * contiguous bits and this function returns those 4 bits as a value.
>> + */
>> +static u64 pmu_format_unpack(u64 format, u64 config_val)
>> +{
>> +       int val_bit = 0;
>> +       u64 res = 0;
>> +       int fmt_bit;
>> +
>> +       for_each_set_bit(fmt_bit, &format, PERF_PMU_FORMAT_BITS) {
>> +               if (test_bit(fmt_bit, &config_val))
>> +                       res |= BIT_ULL(val_bit);
>> +
>> +               val_bit++;
>> +       }
>> +       return res;
>> +}
>> +
>> +int evsel__get_config_val(struct perf_pmu *pmu, struct evsel *evsel,
>> +                         const char *config_name, u64 *val)
> 
> nits:
> This is an evsel__ function but the evsel is the 2nd argument not the first.
> Why pass the PMU and not just read evsel->pmu (or better evsel__find_pmu) ?

That makes sense, I can do that.

> Why not place this in evsel.c to match the header file declaration?

This was for consistency with evsel__set_config_if_unset() that Arnaldo 
moved to pmu.c because of an issue with the Python bindings [1]. That 
doesn't seem to be an issue any more so I could move both to evsel.c. 
That would require making the following things public:

   struct perf_pmu_format
   pmu_format_pack()
   pmu_format_unpack()
   pmu_find_format()

Probably not the end of the world though?

[1]: https://lore.kernel.org/all/ZEbAS2yx2fguW60w@kernel.org/

> The evsel could be likely be const.
> 

Will do

> Thanks,
> Ian
> 
>> +{
>> +       struct perf_pmu_format *format = pmu_find_format(&pmu->format, config_name);
>> +       u64 bits = perf_pmu__format_bits(pmu, config_name);
>> +
>> +       if (!format || !bits) {
>> +               pr_err("Unknown/empty format name: %s\n", config_name);
>> +               *val = 0;
>> +               return -EINVAL;
>> +       }
>> +
>> +       switch (format->value) {
>> +       case PERF_PMU_FORMAT_VALUE_CONFIG:
>> +               *val = pmu_format_unpack(bits, evsel->core.attr.config);
>> +               return 0;
>> +       case PERF_PMU_FORMAT_VALUE_CONFIG1:
>> +               *val = pmu_format_unpack(bits, evsel->core.attr.config1);
>> +               return 0;
>> +       case PERF_PMU_FORMAT_VALUE_CONFIG2:
>> +               *val = pmu_format_unpack(bits, evsel->core.attr.config2);
>> +               return 0;
>> +       case PERF_PMU_FORMAT_VALUE_CONFIG3:
>> +               *val = pmu_format_unpack(bits, evsel->core.attr.config3);
>> +               return 0;
>> +       case PERF_PMU_FORMAT_VALUE_CONFIG4:
>> +               *val = pmu_format_unpack(bits, evsel->core.attr.config4);
>> +               return 0;
>> +       default:
>> +               pr_err("Unknown format value: %d\n", format->value);
>> +               *val = 0;
>> +               return -EINVAL;
>> +       }
>> +}
>> +
>>   /*
>>    * Set @config_name to @val as long as the user hasn't already set or cleared it
>>    * by passing a config term on the command line.
>> @@ -1432,7 +1487,7 @@ void evsel__set_config_if_unset(struct perf_pmu *pmu, struct evsel *evsel,
>>                  return;
>>
>>          /* Otherwise replace it */
>> -       pmu_format_value(&bits, val, vp, /*zero=*/true);
>> +       pmu_format_pack(&bits, val, vp, /*zero=*/true);
>>   }
>>
>>   static struct perf_pmu_format *
>> @@ -1477,8 +1532,8 @@ int perf_pmu__format_type(struct perf_pmu *pmu, const char *name)
>>    * Sets value based on the format definition (format parameter)
>>    * and unformatted value (value parameter).
>>    */
>> -static void pmu_format_value(unsigned long *format, __u64 value, __u64 *v,
>> -                            bool zero)
>> +static void pmu_format_pack(unsigned long *format, __u64 value, __u64 *v,
>> +                           bool zero)
>>   {
>>          unsigned long fbit, vbit;
>>
>> @@ -1595,23 +1650,23 @@ static int pmu_config_term(const struct perf_pmu *pmu,
>>                  switch (term->type_term) {
>>                  case PARSE_EVENTS__TERM_TYPE_CONFIG:
>>                          assert(term->type_val == PARSE_EVENTS__TERM_TYPE_NUM);
>> -                       pmu_format_value(bits, term->val.num, &attr->config, zero);
>> +                       pmu_format_pack(bits, term->val.num, &attr->config, zero);
>>                          break;
>>                  case PARSE_EVENTS__TERM_TYPE_CONFIG1:
>>                          assert(term->type_val == PARSE_EVENTS__TERM_TYPE_NUM);
>> -                       pmu_format_value(bits, term->val.num, &attr->config1, zero);
>> +                       pmu_format_pack(bits, term->val.num, &attr->config1, zero);
>>                          break;
>>                  case PARSE_EVENTS__TERM_TYPE_CONFIG2:
>>                          assert(term->type_val == PARSE_EVENTS__TERM_TYPE_NUM);
>> -                       pmu_format_value(bits, term->val.num, &attr->config2, zero);
>> +                       pmu_format_pack(bits, term->val.num, &attr->config2, zero);
>>                          break;
>>                  case PARSE_EVENTS__TERM_TYPE_CONFIG3:
>>                          assert(term->type_val == PARSE_EVENTS__TERM_TYPE_NUM);
>> -                       pmu_format_value(bits, term->val.num, &attr->config3, zero);
>> +                       pmu_format_pack(bits, term->val.num, &attr->config3, zero);
>>                          break;
>>                  case PARSE_EVENTS__TERM_TYPE_CONFIG4:
>>                          assert(term->type_val == PARSE_EVENTS__TERM_TYPE_NUM);
>> -                       pmu_format_value(bits, term->val.num, &attr->config4, zero);
>> +                       pmu_format_pack(bits, term->val.num, &attr->config4, zero);
>>                          break;
>>                  case PARSE_EVENTS__TERM_TYPE_LEGACY_HARDWARE_CONFIG:
>>                          assert(term->type_val == PARSE_EVENTS__TERM_TYPE_NUM);
>> @@ -1749,7 +1804,7 @@ static int pmu_config_term(const struct perf_pmu *pmu,
>>                   */
>>          }
>>
>> -       pmu_format_value(format->bits, val, vp, zero);
>> +       pmu_format_pack(format->bits, val, vp, zero);
>>          return 0;
>>   }
>>
>>
>> --
>> 2.34.1
>>