selftests/resctrl: Use cache size to determine "fill_buf" buffer size

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@intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

1 files changed, 13 insertions, 0 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;
+}