linux-kernel - Re: [PATCH v6 02/16] selftests/resctrl: Calculate resctrl FS derived mem bw over sleep(1) only

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Date: Fri, 7 Jun 2024 10:54:36 -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>,
	Maciej Wieczór-Retman <maciej.wieczor-retman@...el.com>,
	Babu Moger <babu.moger@....com>
CC: Fenghua Yu <fenghua.yu@...el.com>, <linux-kernel@...r.kernel.org>, "Shuah
 Khan" <skhan@...uxfoundation.org>
Subject: Re: [PATCH v6 02/16] selftests/resctrl: Calculate resctrl FS derived
 mem bw over sleep(1) only

Hi Ilpo,

On 6/7/24 5:53 AM, Ilpo Järvinen wrote:
> For MBM/MBA tests, measure_vals() calls get_mem_bw_imc() that performs
> the measurement over a duration of sleep(1) call. The memory bandwidth
> numbers from IMC are derived over this duration. The resctrl FS derived
> memory bandwidth, however, is calculated inside measure_vals() and only
> takes delta between the previous value and the current one which
> besides the actual test, also samples inter-test noise.
> 
> Rework the logic in measure_vals() and get_mem_bw_imc() such that the
> resctrl FS memory bandwidth section covers much shorter duration
> closely matching that of the IMC perf counters to improve measurement
> accuracy.
> 
> For the second read after rewind() to return a fresh value, also
> newline has to be consumed by the fscanf().
> 
> Suggested-by: Reinette Chatre <reinette.chatre@...el.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Tested-by: Babu Moger <babu.moger@....com>
> ---
> 
> v6:
> - Adjust closing/rollback of the IMC perf
> - Move the comment in measure_vals() to function level
> - Capitalize MBM
> - binded to -> bound to

This change does not match the patch.

> v5:
> - Open mem bw file once and use rewind()
> - Read \n from the mem bw file to allow rewind to return a new value.
> v4:
> - Open resctrl mem bw file (twice) beforehand to avoid opening it during
>    the test
> v3:
> - Don't drop Return: entry from perf_open_imc_mem_bw() func comment
> ---
>   tools/testing/selftests/resctrl/resctrl_val.c | 141 +++++++++++-------
>   1 file changed, 91 insertions(+), 50 deletions(-)
> 
> diff --git a/tools/testing/selftests/resctrl/resctrl_val.c b/tools/testing/selftests/resctrl/resctrl_val.c
> index f55f5989de72..1575c5c09ac7 100644
> --- a/tools/testing/selftests/resctrl/resctrl_val.c
> +++ b/tools/testing/selftests/resctrl/resctrl_val.c
> @@ -306,18 +306,13 @@ static void perf_close_imc_mem_bw(void)
>   }
>   
>   /*
> - * get_mem_bw_imc:	Memory band width as reported by iMC counters
> - * @cpu_no:		CPU number that the benchmark PID is binded to
> - * @bw_report:		Bandwidth report type (reads, writes)
> - *
> - * Memory B/W utilized by a process on a socket can be calculated using
> - * iMC counters. Perf events are used to read these counters.
> + * perf_open_imc_mem_bw - Open perf fds for IMCs
> + * @cpu_no: CPU number that the benchmark PID is bounded to

"is bounded to" -> "is bound to"?

Just the one nitpick from me. The patch looks good to me. Thank you
very much.

| Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette