Re: [PATCH v2 9/9] selftests/resctrl: Reduce L2 impact on CAT test

[Reinette Chatre]

Hi Ilpo,

On 3/6/26 2:35 AM, Ilpo Järvinen wrote:
> On Tue, 3 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>
>> ---
>>  tools/testing/selftests/resctrl/cat_test.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
>> index 6aac03147d41..26062684a9f4 100644
>> --- a/tools/testing/selftests/resctrl/cat_test.c
>> +++ b/tools/testing/selftests/resctrl/cat_test.c
>> @@ -157,6 +157,12 @@ static int cat_test(const struct resctrl_test *test,
>>  	if (ret)
>>  		goto reset_affinity;
>>  
>> +	if (!strcmp(test->resource, "L3") && resctrl_resource_exists("L2")) {
>> +		ret = write_schemata(param->ctrlgrp, "0x1", uparams->cpu, "L2");
>> +		if (ret)
>> +			goto reset_affinity;
>> +	}
> 
> This looks similar to what you did in the CMT test. Maybe add a common 
> function for minimizing L2 cache size so it doesn't have to duplicated to 
> all L3 related tests.

Sure.

Reinette