linux-kernel - Re: [PATCH v2 02/13] selftests/resctrl: Calculate resctrl FS derived mem bw over sleep(1) only

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Date: Mon, 25 Mar 2024 15:08:09 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Reinette Chatre <reinette.chatre@...el.com>
cc: linux-kselftest@...r.kernel.org, Shuah Khan <shuah@...nel.org>, 
    Babu Moger <babu.moger@....com>, 
    Maciej Wieczór-Retman <maciej.wieczor-retman@...el.com>, 
    Fenghua Yu <fenghua.yu@...el.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 02/13] selftests/resctrl: Calculate resctrl FS derived
 mem bw over sleep(1) only

On Fri, 22 Mar 2024, Reinette Chatre wrote:
> On 3/22/2024 5:11 AM, Ilpo Järvinen wrote:
> > On Tue, 19 Mar 2024, Reinette Chatre wrote:
> >> On 3/11/2024 6:52 AM, Ilpo Järvinen wrote:

> >>> + * Return: = 0 on success. < 0 on failure.
> >>> + */
> >>> +static int get_mem_bw_imc(char *bw_report, float *bw_imc)
> >>> +{
> >>> +	float reads, writes, of_mul_read, of_mul_write;
> >>> +	int imc, j;
> >>> +
> >>> +	/* Start all iMC counters to log values (both read and write) */
> >>> +	reads = 0, writes = 0, of_mul_read = 1, of_mul_write = 1;
> >>>  
> >>>  	/*
> >>>  	 * Get results which are stored in struct type imc_counter_config
> > 
> >>> @@ -696,7 +725,6 @@ int resctrl_val(const struct resctrl_test *test,
> >>>  		struct resctrl_val_param *param)
> >>>  {
> >>>  	char *resctrl_val = param->resctrl_val;
> >>> -	unsigned long bw_resc_start = 0;
> >>
> >> In the current implementation the first iteration's starting measurement
> >> is, as seen above, 0 ... which makes the first measurement unreliable
> >> and dropped for both the MBA and MBM tests. In this enhancement, the
> >> first measurement is no longer skewed so much so I wonder if this enhancement
> >> can be expanded to the analysis phase where first measurement no longer
> >> needs to be dropped?
> > 
> > In ideal world, yes, but I'll have to check the raw numbers. My general 
> > feel is that the numbers tend to converge slowly with more iterations 
> > being run so the first iteration might still be "off" by quite much (this 
> > is definitely the case with CAT tests iterations but I'm not entirely sure 
> > any more how it is with other selftests).
> 
> >From what I can tell the CAT test is not dropping any results. It looks
> to me that any "settling" is and should be handled in the test before
> the data collection starts.

It doesn't, but the "settling" is there in the raw numbers. I've 
considered adding warm-up test(s) before the actual runs to improve the 
situation but there's just so many thing still to do...

-- 
 i.