linux-kernel - Re: [PATCH v3 09/16] selftests/resctrl: Simplify mem bandwidth file code for MBA & MBM tests

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Date: Wed, 24 Apr 2024 21:38:22 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	<linux-kselftest@...r.kernel.org>, Shuah Khan <shuah@...nel.org>, Babu Moger
	<babu.moger@....com>, Maciej Wieczór-Retman
	<maciej.wieczor-retman@...el.com>
CC: Fenghua Yu <fenghua.yu@...el.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 09/16] selftests/resctrl: Simplify mem bandwidth file
 code for MBA & MBM tests

Hi Ilpo,

On 4/8/2024 9:32 AM, Ilpo Järvinen wrote:
> initialize_mem_bw_resctrl() and set_mbm_path() contain complicated set
> of conditions, each yielding different file to be opened to measure
> memory bandwidth through resctrl FS. In practice, only two of them are
> used. For MBA test, ctrlgrp is always provided, and for MBM test both
> ctrlgrp and mongrp are set.
> 
> The file used differ between MBA/MBM test, however, MBM test
> unnecessarily create monitor group because resctrl FS already provides
> monitoring interface underneath any ctrlgrp too, which is what the MBA
> selftest uses.
> 
> Consolidate memory bandwidth file used to the one used by the MBA
> selftest. Remove all unused branches opening other files to simplify
> the code.

This is a good change but it seems incomplete to me. As changelog states
MBM creates monitor group unnecessarily, but from what I can tell it continues
to do so after this change. It is also optimized in patch 16, which I think
may end up being dropped as part of cleaning this up (here and for the CMT test).

Reinette