Re: [PATCH] selftests/resctrl: Add non-contiguous CBMs CAT test

[Ilpo Järvinen]

On Thu, 9 Nov 2023, Maciej Wieczor-Retman wrote:

> Non-contiguous CBM support for Intel CAT has been merged into the kernel
> with Commit 0e3cd31f6e90 ("x86/resctrl: Enable non-contiguous CBMs in
> Intel CAT") but there is no selftest that would validate if this feature
> works correctly.
> 
> The selftest needs to verify if writing non-contiguous CBMs to the
> schemata file behaves as expected in comparison to the information about
> non-contiguous CBMs support.
> 
> Add tests for both L2 and L3 CAT to verify if the return values
> generated by writing non-contiguous CBMs don't contradict the
> reported non-contiguous support information.

"if ... don't" sounds weird to me. Perhaps the "if" could just be dropped 
from it.

> Comparing the return value of write_schemata() with non-contiguous CBMs
> support information can be simplified as a logical XOR operation. In
> other words if non-contiguous CBMs are supported and if non-contiguous
> write succeeds the test should succeed and if the write fails the test
> should also fail. The opposite should happen if non-contiguous CBMs are
> not supported.

To me this sounds a bit verbose given how basic thing it talks about 
(but maybe I'm too old already to have actually come across a few xor
tricks in the past :-)). I'd simplify it to (or simply drop it):

Use a logical XOR to confirm return value of write_schemata() and  
non-contiguous CBMs support information match.

> Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx>
> 
> ---
> 
> This patch is based on a rework of resctrl selftests that's currently in
> review [1]. The patch also implements a similiar functionality presented
> in the bash script included in the cover letter to the original
> non-contiguous CBMs in Intel CAT series [2].
> 
> [1] https://lore.kernel.org/all/20231024092634.7122-1-ilpo.jarvinen@xxxxxxxxxxxxxxx/
> [2] https://lore.kernel.org/all/cover.1696934091.git.maciej.wieczor-retman@xxxxxxxxx/
> 
>  tools/testing/selftests/resctrl/cat_test.c    | 97 +++++++++++++++++++
>  tools/testing/selftests/resctrl/resctrl.h     |  2 +
>  .../testing/selftests/resctrl/resctrl_tests.c |  2 +
>  3 files changed, 101 insertions(+)
> 
> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
> index bc88eb891f35..6a01a5da30b4 100644
> --- a/tools/testing/selftests/resctrl/cat_test.c
> +++ b/tools/testing/selftests/resctrl/cat_test.c
> @@ -342,6 +342,87 @@ static int cat_run_test(const struct resctrl_test *test, const struct user_param
>  	return ret;
>  }
>  
> +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, ret, sparse_masks;
> +	char res_path[PATH_MAX];
> +	char schemata[64];
> +	int bit_center;
> +	FILE *fp;
> +
> +	/* Check to compare sparse_masks content to cpuid output. */
> +	snprintf(res_path, sizeof(res_path), "%s/%s/%s", INFO_PATH,
> +		 test->resource, "sparse_masks");
> +
> +	fp = fopen(res_path, "r");
> +	if (!fp) {
> +		perror("# Error in opening file\n");
> +		return errno;
> +	}
> +
> +	if (fscanf(fp, "%u", &sparse_masks) <= 0) {
> +		perror("Could not get sparse_masks contents\n");
> +		fclose(fp);
> +		return -1;
> +	}
> +
> +	fclose(fp);

Add a function to do this conversion into resctrlfs.c.

> +
> +	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;

This would be same as (you need to make the func non-static though):
	level = get_cache_level(test->resource);
	if (level < 0)
		return -EINVAL;
	__cpuid_count(0x10, 4 - level, eax, ebx, ecx, edx);

> +	if (sparse_masks != ((ecx >> 3) & 1))
> +		return -1;
> +
> +	/* Write checks initialization. */
> +	ret = get_cbm_mask(test->resource, &full_cache_mask);
> +	if (ret < 0)
> +		return ret;
> +	bit_center = count_bits(full_cache_mask) / 2;
> +	cont_mask = full_cache_mask >> bit_center;
> +
> +	/* Contiguous mask write check. */
> +	snprintf(schemata, sizeof(schemata), "%lx", cont_mask);
> +	ret = write_schemata("", schemata, uparams->cpu, test->resource);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Non-contiguous mask write check. CBM has a 0xf hole approximately in the middle.
> +	 * Output is compared with support information to catch any edge case errors.
> +	 */
> +	noncont_mask = ~(full_cache_mask & (0xf << bit_center)) & full_cache_mask;

Why is the full_cache_mask & part needed here? It's not like the second 
and can grow bits outside of full_cache_mask even if that would overflow 
the full_cache_mask (it won't be testing hole then though but that 
problem happens also at the boundary condition one bit prior to 
overflowing the mask).

> +	snprintf(schemata, sizeof(schemata), "%lx", noncont_mask);
> +	ret = write_schemata("", schemata, uparams->cpu, test->resource);
> +	if (ret && sparse_masks)
> +		ksft_print_msg("Non-contiguous CBMs supported but write failed\n");
> +	else if (ret && !sparse_masks)
> +		ksft_print_msg("Non-contiguous CBMs not supported and write failed as expected\n");
> +	else if (!ret && !sparse_masks)
> +		ksft_print_msg("Non-contiguous CBMs not supported but write succeeded\n");

Newline.

> +	return !ret == !sparse_masks;
> +}
> +
> +static bool noncont_cat_feature_check(const struct resctrl_test *test)
> +{
> +	char res_path[PATH_MAX];
> +	struct stat statbuf;
> +
> +	snprintf(res_path, sizeof(res_path), "%s/%s/%s", INFO_PATH,
> +		 test->resource, "sparse_masks");
> +
> +	if (stat(res_path, &statbuf))
> +		return false;

This looks generic enough that validate_resctrl_feature_request() should 
be somehow adapted to cover also these cases. Perhaps it would be best to 
just split validate_resctrl_feature_request() into multiple functions.

> +	return test_resource_feature_check(test);
> +}
> +
>  struct resctrl_test l3_cat_test = {
>  	.name = "L3_CAT",
>  	.group = "CAT",
> @@ -357,3 +438,19 @@ struct resctrl_test l2_cat_test = {
>  	.feature_check = test_resource_feature_check,
>  	.run_test = cat_run_test,
>  };
> +
> +struct resctrl_test l3_noncont_cat_test = {
> +	.name = "L3_NONCONT_CAT",
> +	.group = "NONCONT_CAT",

> +struct resctrl_test l2_noncont_cat_test = {
> +	.name = "L2_NONCONT_CAT",
> +	.group = "NONCONT_CAT",

I think these should be grouped among "CAT" group because it well, tests 
CAT functionality. Why you think a separate group for them is needed?

-- 
 i.