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

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Date: Mon, 10 Jun 2024 17:55:23 +0300 (EEST)
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>, 
    Maciej Wieczór-Retman <maciej.wieczor-retman@...el.com>, 
    Babu Moger <babu.moger@....com>, Fenghua Yu <fenghua.yu@...el.com>, 
    LKML <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

On Fri, 7 Jun 2024, Reinette Chatre wrote:
> 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>

I'll correct this in v7. I guess it's because I now make these corrections 
"twice", once for the per patch changelog bullet and then the actual 
change which unfortunately means my brains switch to repeated actions mode 
=> autotype without thinking.

Earlier when I made the version changelogs only into 00/xx, I actually 
read through the diff of diffs against the previous version in order to 
find out what to write into the changelog. I ended up catching many error 
like this in that stage. Now it's just mostly copying the pre-existing 
entries from per patch changelogs (and less attention is obviously paid on 
looking the diff of diffs because I no longer need to derive information
out of them).


-- 
 i.