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

[Reinette Chatre]

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@xxxxxxx>
> ---
> This was part of the series
> https://lore.kernel.org/lkml/cover.1708637563.git.babu.moger@xxxxxxx/
> 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?

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.

Reinette