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

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Date: Thu, 18 Jan 2024 13:02:43 +0100
From: Maciej Wieczór-Retman <maciej.wieczor-retman@...el.com>
To: Reinette Chatre <reinette.chatre@...el.com>
CC: Fenghua Yu <fenghua.yu@...el.com>, Shuah Khan <shuah@...nel.org>,
	<ilpo.jarvinen@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] selftests/resctrl: Add non-contiguous CBMs CAT
 test

On 2024-01-17 at 10:49:06 -0800, Reinette Chatre wrote:
>Hi Maciej,
>
>On 1/17/2024 12:26 AM, Maciej Wieczór-Retman wrote:
>> On 2024-01-08 at 14:42:11 -0800, Reinette Chatre wrote:
>>> On 12/12/2023 6:52 AM, Maciej Wieczor-Retman wrote:
>
>
>>>> +
>>>> +	if (sparse_masks != ((ecx >> 3) & 1))
>>>> +		return -1;
>>>
>>> Can a message be displayed to support the debugging this test failure?
>> 
>> Sure, that is a very good idea. I'll add ksft_perror() here.
>
>I do not think ksft_perror() is appropriate since perror() is for
>system error messages (something that sets errno). Perhaps just
>ksft_print_msg().

Thanks for the suggestion!

>
>>>> +	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;
>>>
>>> How will user know what failed? I am seeing this single test exercise a few scenarios
>>> and it is not obvious to me if the issue will be clear if this test,
>>> noncont_cat_run_test(), fails.
>> 
>> write_schemata() either succeeds with '0' or errors out with a negative value. If
>> the contiguous mask write fails, write_schemata should print out what was wrong
>> and I believe that the test will report an error rather than failure.
>
>Right. I am trying to understand whether the user will be able to decipher what failed
>in case there is an error. Seems like in this case the user is expected to look at the
>source code of the test to understand what the test was trying to do at the time it
>encountered the failure. In this case user may be "lucky" that this test only has
>one write_schemata() call _not_ followed by a ksft_print_msg() so user can use that
>reasoning to figure out which write_schemata() failed to further dig what test was
>trying to do. 

When a write_schemata() is executed the string that is being written gets
printed. If there are multiple calls in a single tests and one fails I'd imagine
it would be easy for the user to figure out which one failed.

On a side note I'm not sure if that's true but I'm getting a feeling that the
harder errors (not just test failures) are more of a clue for developers working
on the tests. Would you agree that it seems like users probably won't see
write_schemata() fail here (if the test execution managed to get to this point
without erroring out due to bad parameters or kernel compiled without required
options)?

>
>Reinette

-- 
Kind regards
Maciej Wieczór-Retman