Re: [PATCH v3 09/10] selftests/resctrl: Simplify perf usage in CAT test

Ilpo Järvinen
2026-03-27T17:48:07Z

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On Fri, 13 Mar 2026, Reinette Chatre wrote:

> The CAT test relies on the PERF_COUNT_HW_CACHE_MISSES event to determine if
> modifying a cache portion size is successful. This event is configured to
> report the data as part of an event group, but no other events are added to
> the group.
>
> Remove the unnecessary PERF_FORMAT_GROUP format setting. This eliminates
> the need for struct perf_event_read and results in read() of the associated
> file descriptor to return just one value associated with the
> PERF_COUNT_HW_CACHE_MISSES event of interest.
>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> Tested-by: Chen Yu <yu.c.chen@intel.com>
> ---
> Changes since v2:
> - Add Chen Yu's tag.
> ---
> tools/testing/selftests/resctrl/cache.c | 17 +++++------------
> tools/testing/selftests/resctrl/cat_test.c | 4 +---
> tools/testing/selftests/resctrl/resctrl.h | 11 +----------
> 3 files changed, 7 insertions(+), 25 deletions(-)
>
> diff --git a/tools/testing/selftests/resctrl/cache.c b/tools/testing/selftests/resctrl/cache.c
> index bef71b6feacc..df9bea584a2d 100644
> --- a/tools/testing/selftests/resctrl/cache.c
> +++ b/tools/testing/selftests/resctrl/cache.c
> @@ -10,7 +10,6 @@ void perf_event_attr_initialize(struct perf_event_attr *pea, __u64 config)
> memset(pea, 0, sizeof(*pea));
> pea->type = PERF_TYPE_HARDWARE;
> pea->size = sizeof(*pea);
> - pea->read_format = PERF_FORMAT_GROUP;
> pea->exclude_kernel = 1;
> pea->exclude_hv = 1;
> pea->exclude_idle = 1;
> @@ -37,19 +36,13 @@ int perf_event_reset_enable(int pe_fd)
> return 0;
> }
>
> -void perf_event_initialize_read_format(struct perf_event_read *pe_read)
> -{
> - memset(pe_read, 0, sizeof(*pe_read));
> - pe_read->nr = 1;
> -}
> -
> int perf_open(struct perf_event_attr *pea, pid_t pid, int cpu_no)
> {
> int pe_fd;
>
> pe_fd = perf_event_open(pea, pid, cpu_no, -1, PERF_FLAG_FD_CLOEXEC);
> if (pe_fd == -1) {
> - ksft_perror("Error opening leader");
> + ksft_perror("Unable to set up performance monitoring");
> return -1;
> }
>
> @@ -132,9 +125,9 @@ static int print_results_cache(const char *filename, pid_t bm_pid, __u64 llc_val
> *
> * Return: =0 on success. <0 on failure.
> */
> -int perf_event_measure(int pe_fd, struct perf_event_read *pe_read,
> - const char *filename, pid_t bm_pid)
> +int perf_event_measure(int pe_fd, const char *filename, pid_t bm_pid)
> {
> + __u64 value;
> int ret;
>
> /* Stop counters after one span to get miss rate */
> @@ -142,13 +135,13 @@ int perf_event_measure(int pe_fd, struct perf_event_read *pe_read,
> if (ret < 0)
> return ret;
>
> - ret = read(pe_fd, pe_read, sizeof(*pe_read));
> + ret = read(pe_fd, &value, sizeof(value));
> if (ret == -1) {
> ksft_perror("Could not get perf value");
> return -1;
> }
>
> - return print_results_cache(filename, bm_pid, pe_read->values[0].value);
> + return print_results_cache(filename, bm_pid, value);
> }
>
> /*
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index 8bc47f06679a..6aac03147d41 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -135,7 +135,6 @@ static int cat_test(const struct resctrl_test *test,
> struct resctrl_val_param *param,
> size_t span, unsigned long current_mask)
> {
> - struct perf_event_read pe_read;
> struct perf_event_attr pea;
> cpu_set_t old_affinity;
> unsigned char *buf;
> @@ -159,7 +158,6 @@ static int cat_test(const struct resctrl_test *test,
> goto reset_affinity;
>
> perf_event_attr_initialize(&pea, PERF_COUNT_HW_CACHE_MISSES);
> - perf_event_initialize_read_format(&pe_read);
> pe_fd = perf_open(&pea, bm_pid, uparams->cpu);
> if (pe_fd < 0) {
> ret = -1;
> @@ -192,7 +190,7 @@ static int cat_test(const struct resctrl_test *test,
>
> fill_cache_read(buf, span, true);
>
> - ret = perf_event_measure(pe_fd, &pe_read, param->filename, bm_pid);
> + ret = perf_event_measure(pe_fd, param->filename, bm_pid);
> if (ret)
> goto free_buf;
> }
> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
> index 3bad2d80c09b..175101022bf3 100644
> --- a/tools/testing/selftests/resctrl/resctrl.h
> +++ b/tools/testing/selftests/resctrl/resctrl.h
> @@ -148,13 +148,6 @@ struct resctrl_val_param {
> struct fill_buf_param *fill_buf;
> };
>
> -struct perf_event_read {
> - __u64 nr; /* The number of events */
> - struct {
> - __u64 value; /* The value of the event */
> - } values[2];
> -};
> -
> /*
> * Memory location that consumes values compiler must not optimize away.
> * Volatile ensures writes to this location cannot be optimized away by
> @@ -210,11 +203,9 @@ unsigned int count_bits(unsigned long n);
> int snc_kernel_support(void);
>
> void perf_event_attr_initialize(struct perf_event_attr *pea, __u64 config);
> -void perf_event_initialize_read_format(struct perf_event_read *pe_read);
> int perf_open(struct perf_event_attr *pea, pid_t pid, int cpu_no);
> int perf_event_reset_enable(int pe_fd);
> -int perf_event_measure(int pe_fd, struct perf_event_read *pe_read,
> - const char *filename, pid_t bm_pid);
> +int perf_event_measure(int pe_fd, const char *filename, pid_t bm_pid);
> int measure_llc_resctrl(const char *filename, pid_t bm_pid);
> int minimize_l2_occupancy(const struct resctrl_test *test,
> const struct user_params *uparams,
>

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

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