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 <[email protected]> > Tested-by: Chen Yu <[email protected]> > --- > 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 <[email protected]> -- i.
