Re: [PATCH] selftests/resctrl: Allow CAT testing when no exclusive cache exists

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Sat, 23 May 2026, Chen Yu wrote:

> The shareable_bits indicates which cache portions might be shared with
> other agents (e.g., GPU, other I/O devices). On some platforms, all L3
> cache ways are marked as potentially shared.
> 
> The L3_CAT test should fall back to using the full CBM mask when no
> exclusive portion exists, since the test logic (writing different
> schemata and measuring cache misses) still works. The shareable mask
> is a hint about potential interference, not a hard exclusion.
> 
> Reported-by: Hongyu Ning <hongyu.ning@linux.intel.com>
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> ---
>  tools/testing/selftests/resctrl/cat_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index f00b622c1460..b6994ba4504b 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -248,7 +248,7 @@ static int cat_run_test(const struct resctrl_test *test, const struct user_param
>  	/* Get the largest contiguous exclusive portion of the cache */
>  	ret = get_mask_no_shareable(test->resource, &long_mask);
>  	if (ret)
> -		return ret;
> +		long_mask = full_cache_mask;

Wouldn't it warrant to log something when the fallback occurs? It 
certainly looks something that makes the results less reliable (so it 
would be nice to know about it when looking at the test results).

>  
>  	/* Get L3/L2 cache size */
>  	ret = get_cache_size(uparams->cpu, test->resource, &cache_total_size);
> 

-- 
 i.