Re: [PATCH v2 1/1] selftests/resctrl: Fix MBM test failure when MBA unavailable

From: Shuah Khan <skhan@linuxfoundation.org>
To: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
	"Reinette Chatre" <reinette.chatre@intel.com>,
	"Shuah Khan" <shuah@kernel.org>
Cc: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-kselftest@vger.kernel.org,
	Fenghua Yu <fenghua.yu@intel.com>,
	Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH v2 1/1] selftests/resctrl: Fix MBM test failure when MBA unavailable
Date: Wed, 18 Oct 2023 13:07:28 -0600	[thread overview]
Message-ID: <2ec50632-15ae-44c3-9851-02660584dd05@linuxfoundation.org> (raw)
In-Reply-To: <9965dc22-16fb-cadc-2b5f-ff7c2c91a173@linux.intel.com>

On 10/18/23 02:10, Ilpo Järvinen wrote:
> On Wed, 18 Oct 2023, Ilpo Järvinen wrote:
> 
>> Commit 20d96b25cc4c ("selftests/resctrl: Fix schemata write error
>> check") exposed a problem in feature detection logic in MBM selftest.
>> If schemata does not support MB:x=x entries, the schemata write to
>> initialize 100% memory bandwidth allocation in mbm_setup() will now
>> fail with -EINVAL due to the error handling corrected by the commit
>> 20d96b25cc4c ("selftests/resctrl: Fix schemata write error check").
>> That commit just uncovers the failed write, it is not wrong itself.
>>
>> If MB:x=x is not supported by schemata, it is safe to assume 100%
>> memory bandwidth is always set. Therefore, the previously ignored error
>> does not make the MBM test itself wrong.
>>
>> Restore the previous behavior of MBM test by checking MB support before
>> attempting to write it into schemata which results in behavior
>> equivalent to ignoring the write error.
>>
>> Fixes: 20d96b25cc4c ("selftests/resctrl: Fix schemata write error check")
>> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
>> Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
>> ---
> 
> It seems it's too early morning for me so I entirely forgot to describe
> the changes I made... doh. So here it is (nothing earth-shattering here
> really):
> 
> v2:
> - Make checkpatch --strict happy.
>    - Remove () that --strict called "extra".
>    - Duplicate the referenced commit description in the changelog
>      to follow the commit formatting guidelines.
>    - Alter the wording at one of the references into the commit
>      20d96b25cc4c in order to avoid having to copy the description
>      there too.
> - Added Reinette's rev-by.
> 

Thank you. Applied to linux-kselftest next for Linux 6.7-rc1

thanks,
-- Shuah