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

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Date:   Fri, 14 Jul 2023 13:22:27 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     "Wieczor-Retman, Maciej" <maciej.wieczor-retman@...el.com>
cc:     Reinette Chatre <reinette.chatre@...el.com>,
        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

On Fri, 14 Jul 2023, Wieczor-Retman, Maciej wrote:

> Hi Reinette!
> 
> 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.

-- 
 i.

> > While MBA, MBM, and CMT tests use resctrl_val() for testing it seems
> > as though the function still exits with the MBA/MBM data recorded in
> > megabytes with the CMT data recorded in bytes. That seems to be why
> > show_mba_info() needs no conversion when displaying the data.
> > 
> > Reinette
> 
> Kind regards
> Maciej Wieczór-Retman
>