On Thu, 17 Oct 2024, Reinette Chatre wrote:
> By default the MBM and MBA tests use the "fill_buf" benchmark to
> read from a buffer with the goal to measure the memory bandwidth
> generated by this buffer access.
>
> Care should be taken when sizing the buffer used by the "fill_buf"
> benchmark. If the buffer is small enough to fit in the cache then
> it cannot be expected that the benchmark will generate much memory
> bandwidth. For example, on a system with 320MB L3 cache the existing
> hardcoded default of 250MB is insufficient.
>
> Use the measured cache size to determine a buffer size that can be
> expected to trigger memory access while keeping the existing default
> as minimum, now renamed to MINIMUM_SPAN, that has been appropriate for
> testing so far.
>
> Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
Look good, thanks.
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
--
i.
> ---
> Changes since V2:
> - Move duplicate code into helper. (Ilpo)
> - Rename DEFAULT_SPAN to MINIMUM_SPAN to reflect its new purpose. (Ilpo)
> - Do _not_ add Ilpo's Reviewed-by tag ... the patch changed too much.
>
> Changes since V1:
> - Ensure buffer is at least double L3 cache size. (Ilpo)
> - Support user override of default buffer size. (Ilpo)
> ---
> tools/testing/selftests/resctrl/fill_buf.c | 13 +++++++++++++
> tools/testing/selftests/resctrl/mba_test.c | 7 ++++++-
> tools/testing/selftests/resctrl/mbm_test.c | 7 ++++++-
> tools/testing/selftests/resctrl/resctrl.h | 3 ++-
> tools/testing/selftests/resctrl/resctrl_tests.c | 2 +-
> 5 files changed, 28 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c
> index 380cc35f10c6..19a01a52dc1a 100644
> --- a/tools/testing/selftests/resctrl/fill_buf.c
> +++ b/tools/testing/selftests/resctrl/fill_buf.c
> @@ -129,3 +129,16 @@ unsigned char *alloc_buffer(size_t buf_size, bool memflush)
>
> return buf;
> }
> +
> +ssize_t get_fill_buf_size(int cpu_no, const char *cache_type)
> +{
> + unsigned long cache_total_size = 0;
> + int ret;
> +
> + ret = get_cache_size(cpu_no, cache_type, &cache_total_size);
> + if (ret)
> + return ret;
> +
> + return cache_total_size * 2 > MINIMUM_SPAN ?
> + cache_total_size * 2 : MINIMUM_SPAN;
> +}
> diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c
> index 74d95c460bd0..bf37f3555660 100644
> --- a/tools/testing/selftests/resctrl/mba_test.c
> +++ b/tools/testing/selftests/resctrl/mba_test.c
> @@ -182,7 +182,12 @@ static int mba_run_test(const struct resctrl_test *test, const struct user_param
> fill_buf.memflush = uparams->fill_buf->memflush;
> param.fill_buf = &fill_buf;
> } else if (!uparams->benchmark_cmd[0]) {
> - fill_buf.buf_size = DEFAULT_SPAN;
> + ssize_t buf_size;
> +
> + buf_size = get_fill_buf_size(uparams->cpu, "L3");
> + if (buf_size < 0)
> + return buf_size;
> + fill_buf.buf_size = buf_size;
> fill_buf.memflush = true;
> param.fill_buf = &fill_buf;
> }
> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c
> index 72261413c868..4224f8ce3538 100644
> --- a/tools/testing/selftests/resctrl/mbm_test.c
> +++ b/tools/testing/selftests/resctrl/mbm_test.c
> @@ -149,7 +149,12 @@ static int mbm_run_test(const struct resctrl_test *test, const struct user_param
> fill_buf.memflush = uparams->fill_buf->memflush;
> param.fill_buf = &fill_buf;
> } else if (!uparams->benchmark_cmd[0]) {
> - fill_buf.buf_size = DEFAULT_SPAN;
> + ssize_t buf_size;
> +
> + buf_size = get_fill_buf_size(uparams->cpu, "L3");
> + if (buf_size < 0)
> + return buf_size;
> + fill_buf.buf_size = buf_size;
> fill_buf.memflush = true;
> param.fill_buf = &fill_buf;
> }
> diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h
> index 032cd9ebd761..a553fe975938 100644
> --- a/tools/testing/selftests/resctrl/resctrl.h
> +++ b/tools/testing/selftests/resctrl/resctrl.h
> @@ -41,7 +41,7 @@
>
> #define BENCHMARK_ARGS 64
>
> -#define DEFAULT_SPAN (250 * MB)
> +#define MINIMUM_SPAN (250 * MB)
>
> /*
> * fill_buf_param: "fill_buf" benchmark parameters
> @@ -169,6 +169,7 @@ int perf_event_open(struct perf_event_attr *hw_event, pid_t pid, int cpu,
> unsigned char *alloc_buffer(size_t buf_size, bool memflush);
> void mem_flush(unsigned char *buf, size_t buf_size);
> void fill_cache_read(unsigned char *buf, size_t buf_size, bool once);
> +ssize_t get_fill_buf_size(int cpu_no, const char *cache_type);
> int initialize_read_mem_bw_imc(void);
> int measure_read_mem_bw(const struct user_params *uparams,
> struct resctrl_val_param *param, pid_t bm_pid);
> diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c
> index 88768f4d4961..790f4eb7871a 100644
> --- a/tools/testing/selftests/resctrl/resctrl_tests.c
> +++ b/tools/testing/selftests/resctrl/resctrl_tests.c
> @@ -189,7 +189,7 @@ static struct fill_buf_param *alloc_fill_buf_param(struct user_params *uparams)
> ksft_exit_skip("Unable to parse benchmark buffer size.\n");
> }
> } else {
> - fill_param->buf_size = DEFAULT_SPAN;
> + fill_param->buf_size = MINIMUM_SPAN;
> }
>
> if (uparams->benchmark_cmd[2]) {
>
