Re: [PATCH v2 24/24] selftests/resctrl: Rewrite Cache Allocation Technology (CAT) test

Hi Ilpo,

On 4/18/2023 4:45 AM, Ilpo Järvinen wrote:

CAT test spawns two processes into two different control groups with exclusive schemata. Both the processes alloc a buffer from memory matching their allocated LLC block size and flush the entire buffer out of caches. Since the processes are reading through the buffer only once during the measurement and initially all the buffer was flushed, the test isn't testing CAT.

Rewrite the CAT test to allocated a buffer sized to half of LLC. Then

"allocated a buffer" -> "allocate a buffer" ?

perform a sequence of tests with different LLC alloc sizes starting from half of the CBM bits down to 1-bit CBM. Flush the buffer before each test and read the buffer twice. Observe the LLC misses on the second read through the buffer. As the allocated LLC block gets smaller and smaller, the LLC misses will become larger and larger giving a strong signal on CAT working properly.

Since the changelog starts by describing the CAT test needing two processes I think it would help to highlight that this test uses a single process. I think it would also help to describing how the cache is used by the rest while this test is running.

Suggested-by: Reinette Chatre reinette.chatre@intel.com Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com

---

tools/testing/selftests/resctrl/cache.c | 20 +- tools/testing/selftests/resctrl/cat_test.c | 204 +++++++++------------ 2 files changed, 97 insertions(+), 127 deletions(-)

diff --git a/tools/testing/selftests/resctrl/cache.c b/tools/testing/selftests/resctrl/cache.c index 7970239413da..64f08ba5edc2 100644 --- a/tools/testing/selftests/resctrl/cache.c +++ b/tools/testing/selftests/resctrl/cache.c @@ -224,10 +224,10 @@ int measure_llc_resctrl(struct resctrl_val_param *param, int bm_pid) */ int cat_val(struct resctrl_val_param *param) {

• int memflush = 1, operation = 0, ret = 0; char *resctrl_val = param->resctrl_val; unsigned long llc_perf_miss = 0; pid_t bm_pid;

• int ret;

if (strcmp(param->filename, "") == 0) sprintf(param->filename, "stdio"); @@ -245,6 +245,10 @@ int cat_val(struct resctrl_val_param *param) if (ret) return ret;

• ret = alloc_buffer(param->span, 1);
• if (ret)

• return ret;
  

• initialize_llc_perf();

/* Test runs until the callback setup() tells the test to stop. */ @@ -256,17 +260,15 @@ int cat_val(struct resctrl_val_param *param) } if (ret < 0) break;

• flush_buffer(param->span);
  

• use_buffer(param->span, 0, true);
  

• ret = reset_enable_llc_perf(bm_pid, param->cpu_no); if (ret) break;

• if (run_fill_buf(param->span, memflush, operation, true)) {
  

• 	fprintf(stderr, "Error-running fill buffer\n");
  

• 	ret = -1;
  

• 	break;
  

• }
  

• sleep(1);
  

• use_buffer(param->span, 0, true);
  

/* Measure cache miss from perf */ ret = get_llc_perf(&llc_perf_miss); @@ -279,6 +281,8 @@ int cat_val(struct resctrl_val_param *param) break; }

• free_buffer();
• return ret;

} diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c index 4b505fdb35d7..85053829b9c5 100644 --- a/tools/testing/selftests/resctrl/cat_test.c +++ b/tools/testing/selftests/resctrl/cat_test.c @@ -11,11 +11,12 @@ #include "resctrl.h" #include <unistd.h> -#define RESULT_FILE_NAME1 "result_cat1" -#define RESULT_FILE_NAME2 "result_cat2" -#define NUM_OF_RUNS 5 -#define MAX_DIFF_PERCENT 4 -#define MAX_DIFF 1000000 +#define RESULT_FILE_NAME "result_cat" +#define NUM_OF_RUNS 5 +#define MIN_DIFF_PERCENT_PER_BIT 2

Could you please start a new trend that adds documentation that explains what this constant means and how it was chosen?

+static unsigned long current_mask; +static long prev_avg_llc_val; /*

• Change schemata. Write schemata to specified

@@ -28,13 +29,24 @@ static int cat_setup(struct resctrl_val_param *p) int ret = 0; /* Run NUM_OF_RUNS times */

• if (p->num_of_runs >= NUM_OF_RUNS)

• return END_OF_TESTS;
  

• if (p->num_of_runs >= NUM_OF_RUNS) {

• /* Remove one bit from the consecutive block */
  

• current_mask &= current_mask >> 1;
  

• if (!current_mask)
  

• 	return END_OF_TESTS;
  

• p->num_of_runs = 0;
  

This seems like a workaround to get the schemata to be written. It is problematic since now p->num_of_runs no longer accurately reflects the number of test runs. I was expecting this mask manipulation to be in cat_val() so that it is clear how test works instead of part of the logic handled here.

• }

if (p->num_of_runs == 0) {

• sprintf(schemata, "%lx", p->mask);
  

• ret = write_schemata(p->ctrlgrp, schemata, p->cpu_no,
  

• 		     p->resctrl_val);
  

• snprintf(schemata, sizeof(schemata), "%lx", p->mask & ~current_mask);
  

• ret = write_schemata("", schemata, p->cpu_no, p->resctrl_val);
  

• if (ret)
  

• 	return ret;
  

• snprintf(schemata, sizeof(schemata), "%lx", current_mask);
  

• ret = write_schemata(p->ctrlgrp, schemata, p->cpu_no, p->resctrl_val);
  

• if (ret)
  

• 	return ret;
  

  } p->num_of_runs++;

...

@@ -126,7 +162,7 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type) ret = get_mask_no_shareable(cache_type, &long_mask); if (ret) return ret;

• count_of_bits = count_consecutive_bits(long_mask, NULL);

• count_of_bits = count_consecutive_bits(long_mask, &start);

/* Get L3/L2 cache size */ ret = get_cache_size(cpu_no, cache_type, &cache_size); @@ -143,99 +179,29 @@ int cat_perf_miss_val(int cpu_no, int n, char *cache_type) count_of_bits - 1); return -1; }

• /* Get core id from same socket for running another thread */
• sibling_cpu_no = get_core_sibling(cpu_no);

Do any users of get_core_sibling() remain after this?

Reinette