linux-kernel - Re: [PATCH 1/1] selftests/resctrl: Don't fail MBM test when schemata doesn't support MB:x=x line

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Message-ID: <fc9266f3-ea4b-4df5-82ab-697ca6742176@intel.com>
Date:   Tue, 17 Oct 2023 09:17:55 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH 1/1] selftests/resctrl: Don't fail MBM test when schemata
 doesn't support MB:x=x line

Hi Ilpo,

The subject could be shortened to:
selftests/resctrl: Fix MBM test failure when MBA unavailable

On 10/17/2023 5:17 AM, 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 20d96b25cc4c.
> Commit 20d96b25cc4c 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@...ux.intel.com>
> ---
>  tools/testing/selftests/resctrl/mbm_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/resctrl/mbm_test.c b/tools/testing/selftests/resctrl/mbm_test.c
> index d3c0d30c676a..85987957e7f5 100644
> --- a/tools/testing/selftests/resctrl/mbm_test.c
> +++ b/tools/testing/selftests/resctrl/mbm_test.c
> @@ -95,7 +95,7 @@ static int mbm_setup(struct resctrl_val_param *p)
>  		return END_OF_TESTS;
>  
>  	/* Set up shemata with 100% allocation on the first run. */
> -	if (p->num_of_runs == 0)
> +	if ((p->num_of_runs == 0) && validate_resctrl_feature_request("MB", NULL))
>  		ret = write_schemata(p->ctrlgrp, "100", p->cpu_no,
>  				     p->resctrl_val);
>  

Thank you for catching this.

Could you please ensure that this patch passes a "checkpatch.pl --strict" check?
With that addressed:
Reviewed-by: Reinette Chatre <reinette.chatre@...el.com> 

Reinette