linux-kernel - Re: [PATCH v4 10/19] selftests/resctrl: Express span internally in bytes

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Message-ID: <f1233835-8c94-e110-531f-13712569b7c0@intel.com>
Date:   Fri, 14 Jul 2023 10:38:21 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        "Wieczor-Retman, Maciej" <maciej.wieczor-retman@...el.com>
CC:     <linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>,
        Shaopeng Tan <tan.shaopeng@...fujitsu.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 10/19] selftests/resctrl: Express span internally in
 bytes

Hi Ilpo,

On 7/14/2023 3:22 AM, Ilpo Järvinen wrote:
> On Fri, 14 Jul 2023, Wieczor-Retman, Maciej wrote:
>> On 14.07.2023 01:00, Reinette Chatre wrote:
>>> Hi Ilpo,
>>>
>>> On 7/13/2023 6:19 AM, Ilpo Järvinen wrote:
>>>> MBA and MBM tests to use megabytes to represent span. CMT test uses
>>>> bytes. The difference requires run_benchmark() to size the buffer
>>>> differently based on the test name, which in turn requires passing the
>>>> test name into run_benchmark().
>>>>
>>>> Convert MBA and MBM tests to use internally bytes like CMT test to
>>>> remove the internal inconsistency between the tests. Remove the test
>>>> dependent buffer sizing from run_benchmark().
>>>
>>> If I understand correctly the intention is to always use bytes internally
>>> and only convert to megabytes when displayed to user space. The above
>>> implies that this takes care of the conversion but there still seems
>>> to be places that that do not follow my understanding. For example,
>>> resctrl_val.c:measure_vals() converts to megabytes before proceeding.
>>
>> Doesn't the use case inside resctrl_val.c:measure_vals() satisfy
>> the idea of only displaying data to the user space? From my
>> understanding it reads the number of bytes and only converts to
>> MB when printing the value. Or did I miss some detail there?
> 
> It's for printing there yes.
> 
> But it's not about span in the first place so I'm not sure why it is 
> related.
> 

If this change is just about how "span" is interpreted by the different
tests then the changelog could be more specific to not create expectation
that with this change there are no longer "bytes vs megabytes" internal
inconsistency between MBA, MBM, and CMT tests.

Reinette