Hi Richard,
On 5/28/26 7:23 PM, Richard Cheng wrote:
> L3_CAT measures cache isolation, which requires at least one cache bit
> that is not shared with non-CPU agents, i.e. cbm_mask & ~shareable_bits
> must be non-zero. On MPAM, shareable_bits == cbm_mask is a legitimate
> state, so there are situations in which no bit can be reported as
> exclusive.
To make problem clear, please append "... causing the L3_CAT test to fail."
>
> Previously get_mask_no_shareable() was invoked inside cat_run_test()
Written in past tense is confusing since it describes current behavior.
> and silently returned -1, which surfaced as a test failure on arm64
> MPAM systems.
>
> Implement cat_feature_check() to perform the same check at feature-check
> time. It prints a diagnostic and returns false so the test case is
> skipped instead of failing.
The second and third paragraph describes a lot of detail that is clear from
the patch. I think these two paragraphs can just be replaced with something
brief like:
Skip, don't fail, the L3_CAT test when the platform does not have any
cache portions that the test can use.
>
> Tested-by: Chen Yu <[email protected]>
> Signed-off-by: Richard Cheng <[email protected]>
> Reviewed-by: Ilpo Järvinen <[email protected]>
> ---
> tools/testing/selftests/resctrl/cat_test.c | 23 +++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/resctrl/cat_test.c
> b/tools/testing/selftests/resctrl/cat_test.c
> index f00b622c1460..dc414e55ae94 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -378,11 +378,32 @@ static bool noncont_cat_feature_check(const struct
> resctrl_test *test)
> return resource_info_file_exists(test->resource, "sparse_masks");
> }
>
> +static bool cat_feature_check(const struct resctrl_test *test)
> +{
> + unsigned long mask;
> +
> + if (!test_resource_feature_check(test))
> + return false;
> +
> + /*
> + * The CAT isolation measurement needs a cache portion that no
> + * other agent shares. On MPAM the kernel may legitimately report
This does not seem to be unique to MPAM
(https://lore.kernel.org/lkml/[email protected]/)
Perhaps "On MPAM the kernel may" -> "Some platforms may"?
> + * all bits as shareable; skip the test if that is the case.
> + */
> + if (get_mask_no_shareable(test->resource, &mask)) {
> + ksft_print_msg("All %s bits are shareable; cannot measure CAT
> isolation\n",
> + test->resource);
> + return false;
> + }
> +
> + return true;
> +}
> +
> struct resctrl_test l3_cat_test = {
> .name = "L3_CAT",
> .group = "CAT",
> .resource = "L3",
> - .feature_check = test_resource_feature_check,
> + .feature_check = cat_feature_check,
> .run_test = cat_run_test,
> .cleanup = cat_test_cleanup,
> };
Patch looks good to me, thank you.
Reinette
