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

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Message-ID: <05db3bdc-9d54-44d2-8aae-07d66053892e@intel.com>
Date: Thu, 18 Jan 2024 09:15:46 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Maciej Wieczór-Retman <maciej.wieczor-retman@...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

Hi Maciej,

On 1/18/2024 4:02 AM, Maciej Wieczór-Retman wrote:
> On 2024-01-17 at 10:49:06 -0800, Reinette Chatre wrote:
>> 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:

>>>>> +	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.

It would be easy for the user the figure out if (a) it is obvious to the user
what schema a particular write_schema() call attempted to write and (b) all the
write_schema() calls attempt to write different schema.

> 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)?

I do agree that users probably won't see such failures. I do not think these
errors are clues to developers working on the tests though, but instead clues
to resctrl developers or kernel development CI systems.

Reinette