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

Ian Rogers
2025-12-16T20:44:52Z

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) ?
Why not place this in evsel.c to match the header file declaration?
The evsel could be likely be const.

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
>