Re: [PATCH v3 05/10] selftests/resctrl: Support multiple events associated with iMC

Ilpo Järvinen
2026-03-27T17:29:01Z

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On Fri, 13 Mar 2026, Reinette Chatre wrote:

> The resctrl selftests discover needed parameters to perf_event_open() via
> sysfs. The PMU associated with every memory controller (iMC) is discovered
> via the /sys/bus/event_source/devices/uncore_imc_N/type file while
> the read memory bandwidth event type and umask is discovered via
> /sys/bus/event_source/devices/uncore_imc_N/events/cas_count_read.
>
> Newer systems may have multiple events that expose read memory bandwidth.
> Running a recent kernel that includes
> commit 6a8a48644c4b ("perf/x86/intel/uncore: Add per-scheduler IMC CAS count events")
> on these systems expose the multiple events. For example,
> /sys/bus/event_source/devices/uncore_imc_N/events/cas_count_read_sch0
> /sys/bus/event_source/devices/uncore_imc_N/events/cas_count_read_sch1
>
> Support parsing of iMC PMU properties when the PMU may have multiple events
> to measure read memory bandwidth. The PMU only needs to be discovered once.
> Split the parsing of event details from actual PMU discovery in order to
> loop over all events associated with the PMU. Match all events with the
> cas_count_read prefix instead of requiring there to be one file with that
> name.
>
> Make the parsing code more robust. With strings passed around to create
> needed paths, use snprintf() instead of sprintf() to ensure there is
> always enough space to create the path while using the standard PATH_MAX
> for path lengths. Ensure there is enough room in imc_counters_config[]
> before attempting to add an entry.
>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> Tested-by: Chen Yu <yu.c.chen@intel.com>
> Reviewed-by: Zide Chen <zide.chen@intel.com>

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

--
i.

> ---
> Changes since v1:
> - Add Zide Chen's RB tag.
>
> Changes since v2:
> - Update changelog to note merged perf change that supports this change.
> - Use PATH_MAX instead of magic number for path lengths. (Ilpo)
> - Rename "org_count" -> "orig_count". (Ilpo)
> - Rework flow surrounding fscanf() used in both parse_imc_read_bw_events()
> and read_from_imc_dir(). (Ilpo)
> - Handle error first to reduce indentation. (Ilpo)
> - Add Chen Yu's tag.
> ---
> tools/testing/selftests/resctrl/resctrl_val.c | 118 ++++++++++++++----
> 1 file changed, 93 insertions(+), 25 deletions(-)
>
> diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
> index 6d766347e3fc..f20d2194c35f 100644
> --- a/tools/testing/selftests/resctrl/resctrl_val.c
> +++ b/tools/testing/selftests/resctrl/resctrl_val.c
> @@ -11,10 +11,10 @@
> #include "resctrl.h"
>
> #define UNCORE_IMC "uncore_imc"
> -#define READ_FILE_NAME "events/cas_count_read"
> +#define READ_FILE_NAME "cas_count_read"
> #define DYN_PMU_PATH "/sys/bus/event_source/devices"
> #define SCALE 0.00006103515625
> -#define MAX_IMCS 20
> +#define MAX_IMCS 40
> #define MAX_TOKENS 5
>
> #define CON_MBM_LOCAL_BYTES_PATH \
> @@ -109,46 +109,114 @@ static int open_perf_read_event(int i, int cpu_no)
> return 0;
> }
>
> -/* Get type and config of an iMC counter's read event. */
> -static int read_from_imc_dir(char *imc_dir, unsigned int *count)
> +static int parse_imc_read_bw_events(char *imc_dir, unsigned int type,
> + unsigned int *count)
> {
> - char cas_count_cfg[1024], imc_counter_cfg[1024], imc_counter_type[1024];
> + char imc_events_dir[PATH_MAX], imc_counter_cfg[PATH_MAX];
> + unsigned int orig_count = *count;
> + char cas_count_cfg[1024];
> + struct dirent *ep;
> + int path_len;
> + int ret = -1;
> + int num_cfg;
> FILE *fp;
> + DIR *dp;
>
> - /* Get type of iMC counter */
> - sprintf(imc_counter_type, "%s%s", imc_dir, "type");
> - fp = fopen(imc_counter_type, "r");
> - if (!fp) {
> - ksft_perror("Failed to open iMC counter type file");
> + path_len = snprintf(imc_events_dir, sizeof(imc_events_dir), "%sevents",
> + imc_dir);
> + if (path_len >= sizeof(imc_events_dir)) {
> + ksft_print_msg("Unable to create path to %sevents\n", imc_dir);
> + return -1;
> + }
>
> + dp = opendir(imc_events_dir);
> + if (!dp) {
> + ksft_perror("Unable to open PMU events directory");
> return -1;
> }
> - if (fscanf(fp, "%u", &imc_counters_config[*count].type) <= 0) {
> - ksft_perror("Could not get iMC type");
> +
> + while ((ep = readdir(dp))) {
> + /*
> + * Parse all event files with READ_FILE_NAME prefix that
> + * contain the event number and umask. Skip files containing
> + * "." that contain unused properties of event.
> + */
> + if (!strstr(ep->d_name, READ_FILE_NAME) ||
> + strchr(ep->d_name, '.'))
> + continue;
> +
> + path_len = snprintf(imc_counter_cfg, sizeof(imc_counter_cfg),
> + "%s/%s", imc_events_dir, ep->d_name);
> + if (path_len >= sizeof(imc_counter_cfg)) {
> + ksft_print_msg("Unable to create path to %s/%s\n",
> + imc_events_dir, ep->d_name);
> + goto out_close;
> + }
> + fp = fopen(imc_counter_cfg, "r");
> + if (!fp) {
> + ksft_perror("Failed to open iMC config file");
> + goto out_close;
> + }
> + num_cfg = fscanf(fp, "%1023s", cas_count_cfg);
> fclose(fp);
> + if (num_cfg <= 0) {
> + ksft_perror("Could not get iMC cas count read");
> + goto out_close;
> + }
> + if (*count >= MAX_IMCS) {
> + ksft_print_msg("Maximum iMC count exceeded\n");
> + goto out_close;
> + }
>
> - return -1;
> + imc_counters_config[*count].type = type;
> + get_read_event_and_umask(cas_count_cfg, *count);
> + /* Do not fail after incrementing *count. */
> + *count += 1;
> }
> - fclose(fp);
> + if (*count == orig_count) {
> + ksft_print_msg("Unable to find events in %s\n", imc_events_dir);
> + goto out_close;
> + }
> + ret = 0;
> +out_close:
> + closedir(dp);
> + return ret;
> +}
>
> - /* Get read config */
> - sprintf(imc_counter_cfg, "%s%s", imc_dir, READ_FILE_NAME);
> - fp = fopen(imc_counter_cfg, "r");
> - if (!fp) {
> - ksft_perror("Failed to open iMC config file");
> +/* Get type and config of an iMC counter's read event. */
> +static int read_from_imc_dir(char *imc_dir, unsigned int *count)
> +{
> + char imc_counter_type[PATH_MAX];
> + unsigned int type;
> + int path_len;
> + FILE *fp;
> + int ret;
>
> + /* Get type of iMC counter */
> + path_len = snprintf(imc_counter_type, sizeof(imc_counter_type),
> + "%s%s", imc_dir, "type");
> + if (path_len >= sizeof(imc_counter_type)) {
> + ksft_print_msg("Unable to create path to %s%s\n",
> + imc_dir, "type");
> return -1;
> }
> - if (fscanf(fp, "%1023s", cas_count_cfg) <= 0) {
> - ksft_perror("Could not get iMC cas count read");
> - fclose(fp);
> + fp = fopen(imc_counter_type, "r");
> + if (!fp) {
> + ksft_perror("Failed to open iMC counter type file");
>
> return -1;
> }
> + ret = fscanf(fp, "%u", &type);
> fclose(fp);
> -
> - get_read_event_and_umask(cas_count_cfg, *count);
> - *count += 1;
> + if (ret <= 0) {
> + ksft_perror("Could not get iMC type");
> + return -1;
> + }
> + ret = parse_imc_read_bw_events(imc_dir, type, count);
> + if (ret) {
> + ksft_print_msg("Unable to parse bandwidth event and umask\n");
> + return ret;
> + }
>
> return 0;
> }
>