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

From: Reinette Chatre
Date: Thu Jun 06 2024 - 16:37:07 EST


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