Re: [PATCH v3 10/10] selftests/resctrl: Reduce L2 impact on CAT test

[Ilpo Järvinen]

On Fri, 13 Mar 2026, Reinette Chatre wrote:

> The L3 CAT test loads a buffer into cache that is proportional to the L3
> size allocated for the workload and measures cache misses when accessing
> the buffer as a test of L3 occupancy. When loading the buffer it can be
> assumed that a portion of the buffer will be loaded into the L2 cache and
> depending on cache design may not be present in L3. It is thus possible
> for data to not be in L3 but also not trigger an L3 cache miss when
> accessed.
> 
> Reduce impact of L2 on the L3 CAT test by, if L2 allocation is supported,
> minimizing the portion of L2 that the workload can allocate into. This
> encourages most of buffer to be loaded into L3 and support better
> comparison between buffer size, cache portion, and cache misses when
> accessing the buffer.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Tested-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> ---
> Changes since v2:
> - Add Chen Yu's tag.
> ---
>  tools/testing/selftests/resctrl/cat_test.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index 6aac03147d41..371a2f26dc47 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -157,6 +157,10 @@ static int cat_test(const struct resctrl_test *test,
>  	if (ret)
>  		goto reset_affinity;
>  
> +	ret = minimize_l2_occupancy(test, uparams, param);
> +	if (ret)
> +		goto reset_affinity;
> +
>  	perf_event_attr_initialize(&pea, PERF_COUNT_HW_CACHE_MISSES);
>  	pe_fd = perf_open(&pea, bm_pid, uparams->cpu);
>  	if (pe_fd < 0) {
> 

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>

-- 
 i.