linux-kernel - Re: [PATCH v2 4/4] selftests/resctrl: Add non-contiguous CBMs CAT test

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Date: Tue, 9 Jan 2024 09:17:42 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, Fenghua Yu
	<fenghua.yu@...el.com>, Shuah Khan <shuah@...nel.org>, LKML
	<linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] selftests/resctrl: Add non-contiguous CBMs CAT
 test

Hi Ilpo,

On 1/9/2024 1:13 AM, Ilpo Järvinen wrote:
> On Mon, 8 Jan 2024, Reinette Chatre wrote:
> 
>> Hi Maciej,
>>
>> On 12/12/2023 6:52 AM, Maciej Wieczor-Retman wrote:
>>> Add tests for both L2 and L3 CAT to verify the return values
>>> generated by writing non-contiguous CBMs don't contradict the
>>> reported non-contiguous support information.
>>>
>>> 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@...el.com>
>>> ---
>>> Changelog v2:
>>> - Redo the patch message. (Ilpo)
>>> - Tidy up __cpuid_count calls. (Ilpo)
>>> - Remove redundant AND in noncont_mask calculations (Ilpo)
>>> - Fix bit_center offset.
>>> - Add newline before function return. (Ilpo)
>>> - Group non-contiguous tests with CAT tests. (Ilpo)
>>> - Use a helper for reading sparse_masks file. (Ilpo)
>>> - Make get_cache_level() available in other source files. (Ilpo)
>>>
>>>  tools/testing/selftests/resctrl/cat_test.c    | 75 +++++++++++++++++++
>>>  tools/testing/selftests/resctrl/resctrl.h     |  3 +
>>>  .../testing/selftests/resctrl/resctrl_tests.c |  2 +
>>>  tools/testing/selftests/resctrl/resctrlfs.c   |  2 +-
>>>  4 files changed, 81 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/tools/testing/selftests/resctrl/cat_test.c b/tools/testing/selftests/resctrl/cat_test.c
>>> index 7dc7206b3b99..ecf553a89aae 100644
>>> --- a/tools/testing/selftests/resctrl/cat_test.c
>>> +++ b/tools/testing/selftests/resctrl/cat_test.c
>>> @@ -292,6 +292,65 @@ 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;
>>> +	int level, bit_center, sparse_masks;
>>> +	char schemata[64];
>>> +
>>> +	/* Check to compare sparse_masks content to cpuid output. */
>>
>> "cpuid" -> "CPUID" (to note it is an instruction)
>>
>>> +	sparse_masks = read_info_res_file(test->resource, "sparse_masks");
>>> +	if (sparse_masks < 0)
>>> +		return sparse_masks;
>>> +
>>> +	level = get_cache_level(test->resource);
>>> +	if (level < 0)
>>> +		return -EINVAL;
>>> +	__cpuid_count(0x10, 4 - level, eax, ebx, ecx, edx);
>>
>> Please do not invent relationships. Please replace the "4 - level" with
>> specific index used that depends on particular cache. The cache level
>> may not even be needed, just use the resource to determine the correct
>> index.
> 
> This is actually my fault, I suggested Maciej could use arithmetics there.

No problem. The math works for the current values but there is no such
relationship. If hypothetically a new cache level needs to be supported
then this computation cannot be relied upon to continue to be correct.

>>> +	return !ret == !sparse_masks;
>>
>> Please return negative on error. Ilpo just did a big cleanup to address this.
> 
> Test failure is not same as an error. So tests should return negative for 
> errors which prevent even running test at all, and 0/1 for test 
> success/fail.
> 

Thanks for catching this. I missed this subtlety in the framework.

Reinette