Re: [PATCH] selftests/resctrl: Fix noncont_cat_run_test for AMD

["Moger, Babu" <bmoger@amd.com>]

Hi Reinette,

On 6/6/2024 6:58 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 6/6/24 4:09 PM, Moger, Babu wrote:
>> Hi Reinette,
>>
>>
>> On 6/6/2024 3:33 PM, Reinette Chatre wrote:
>>> Hi Babu,
>>>
>>> On 6/5/24 2:36 PM, Babu Moger wrote:
>>>> The selftest noncont_cat_run_test fails on AMD with the warnings. 
>>>> Reason
>>>> is, AMD supports non contiguous CBM masks but does not report it via 
>>>> CPUID.
>>>>
>>>> Update noncont_cat_run_test to check for the vendor when verifying 
>>>> CPUID.
>>>>
>>>> Fixes: ae638551ab64 ("selftests/resctrl: Add non-contiguous CBMs CAT 
>>>> test")
>>>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>>>> ---
>>>> This was part of the series
>>>> https://lore.kernel.org/lkml/cover.1708637563.git.babu.moger@amd.com/
>>>> Sending this as a separate fix per review comments.
>>>> ---
>>>>   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 d4dffc934bc3..b2988888786e 100644
>>>> --- a/tools/testing/selftests/resctrl/cat_test.c
>>>> +++ b/tools/testing/selftests/resctrl/cat_test.c
>>>> @@ -308,7 +308,7 @@ static int noncont_cat_run_test(const struct 
>>>> resctrl_test *test,
>>>>       else
>>>>           return -EINVAL;
>>>> -    if (sparse_masks != ((ecx >> 3) & 1)) {
>>>> +    if ((get_vendor() == ARCH_INTEL) && sparse_masks != ((ecx >> 3) 
>>>> & 1)) {
>>>>           ksft_print_msg("CPUID output doesn't match 'sparse_masks' 
>>>> file content!\n");
>>>>           return 1;
>>>>       }
>>>
>>> Since AMD does not report this support via CPUID it does not seem
>>> appropriate to use CPUID at all on AMD when doing the hardware check.
>>> I think the above check makes it difficult to understand what is 
>>> different
>>> on AMD.
>>>
>>> What if instead there is a new function, for example,
>>> "static bool arch_supports_noncont_cat(const struct resctrl_test *test)"
>>> that returns true if the hardware supports non-contiguous CBM?
>>
>> Sure.
>>
>>>
>>> The vendor check can be in there to make it obvious what is going on:
>>>
>>>      /* AMD always supports non-contiguous CBM. */
>>>      if (get_vendor() == AMD)
>>>          return true;
>>>
>>>      /* CPUID check for Intel here. */
>>>
>>> The "sparse_masks" from kernel can then be checked against
>>> hardware support with an appropriate (no mention of CPUID)
>>> error message if this fails.
>>>
>>
>> Something like this?
>>
>>
>> diff --git a/tools/testing/selftests/resctrl/cat_test.c 
>> b/tools/testing/selftests/resctrl/cat_test.c
>> index d4dffc934bc3..b75d220f29f6 100644
>> --- a/tools/testing/selftests/resctrl/cat_test.c
>> +++ b/tools/testing/selftests/resctrl/cat_test.c
>> @@ -288,11 +288,30 @@ static int cat_run_test(const struct 
>> resctrl_test *test, const struct user_param
>>          return ret;
>>   }
>>
>> +static bool arch_supports_noncont_cat(const struct resctrl_test *test)
>> +{
>> +       unsigned int eax, ebx, ecx, edx;
>> +
>> +       /* AMD always supports non-contiguous CBM. */
>> +       if (get_vendor() == ARCH_AMD) {
>> +               return true;
>> +       } else {
> 
> The else can be dropped since it follows a return.
Sure

> The rest of the code can be prefixed with a matching
> comment like:
>      /* Intel support for non-contiguous CBM needs to be discovered. */

Sure
> 
> (please feel free to improve)
> 
>> +               if (!strcmp(test->resource, "L3"))
>> +                       __cpuid_count(0x10, 1, eax, ebx, ecx, edx);
>> +               else if (!strcmp(test->resource, "L2"))
>> +                       __cpuid_count(0x10, 2, eax, ebx, ecx, edx);
>> +               else
>> +                       return false;
>> +
>> +               return ((ecx >> 3) & 1);
>> +       }
>> +}
>> +
>>   static int noncont_cat_run_test(const struct resctrl_test *test,
>>                                  const struct user_params *uparams)
>>   {
>>          unsigned long full_cache_mask, cont_mask, noncont_mask;
>> -       unsigned int eax, ebx, ecx, edx, sparse_masks;
>> +       unsigned int sparse_masks;
>>          int bit_center, ret;
>>          char schemata[64];
>>
>> @@ -301,15 +320,8 @@ static int noncont_cat_run_test(const struct 
>> resctrl_test *test,
>>          if (ret)
>>                  return ret;
>>
>> -       if (!strcmp(test->resource, "L3"))
>> -               __cpuid_count(0x10, 1, eax, ebx, ecx, edx);
>> -       else if (!strcmp(test->resource, "L2"))
>> -               __cpuid_count(0x10, 2, eax, ebx, ecx, edx);
>> -       else
>> -               return -EINVAL;
>> -
>> -       if (sparse_masks != ((ecx >> 3) & 1)) {
>> -               ksft_print_msg("CPUID output doesn't match 
>> 'sparse_masks' file content!\n");
>> +       if (!(arch_supports_noncont_cat(test) && sparse_masks)) {
>> +               ksft_print_msg("Hardware does not support 
>> non-contiguous CBM!\n");
> 
> Please fix the test as well as the message. It is not an error if 
> hardware does
> not support non-contiguous CBM. It is an error if the hardware and 
> kernel disagrees whether
> non-contiguous CBM is supported.

Not sure about this comment.

Did you mean?

  if (!arch_supports_noncont_cat(test)) {
                 ksft_print_msg("Hardware does not support 
non-contiguous CBM!\n");
                 return 0;
          } else if (arch_supports_noncont_cat(test) && !sparse_masks)) {
                 ksft_print_msg("Hardware and kernel support for 
non-contiguous CBM does not match!\n");
                 return 1;
         }


-- 
- Babu Moger