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

["Chen, Yu C" <yu.c.chen@intel.com>]

Hi Ilpo,

On 5/25/2026 6:01 PM, Ilpo Järvinen wrote:
> 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).
> 

Got it. Let me add the following message:
ksft_print_msg("No exclusive cache portion found, fall back to full 
cache mask\n");

thanks,
Chenyu