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From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>
Date: Fri, 31 May 2024 15:51:44 +0300 (EEST)
To: Reinette Chatre <reinette.chatre@intel.com>
cc: linux-kselftest@vger.kernel.org, Shuah Khan <shuah@kernel.org>, 
    Babu Moger <babu.moger@amd.com>, 
    =?ISO-8859-15?Q?Maciej_Wiecz=F3r-Retman?= <maciej.wieczor-retman@intel.com>, 
    LKML <linux-kernel@vger.kernel.org>, Fenghua Yu <fenghua.yu@intel.com>, 
    Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH v4 02/16] selftests/resctrl: Calculate resctrl FS derived
 mem bw over sleep(1) only
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On Thu, 30 May 2024, Reinette Chatre wrote:

> Hi Ilpo,
>=20
> On 5/30/24 4:11 AM, Ilpo J=E4rvinen wrote:
> > On Tue, 28 May 2024, Reinette Chatre wrote:
> > > On 5/28/24 3:19 AM, Ilpo J=E4rvinen wrote:
> > > > On Fri, 24 May 2024, Ilpo J=E4rvinen wrote:
> > > > > On Fri, 24 May 2024, Reinette Chatre wrote:
> > > > > > On 5/24/24 12:57 AM, Ilpo J=E4rvinen wrote:
> > > > > > > On Thu, 23 May 2024, Reinette Chatre wrote:
>=20
> ...
>=20
> > > > > > It is not necessary to open and close the file every time a val=
ue
> > > > > > needs
> > > > > > to be read from it.
> > > >=20
> > > > I'm bit unsure where to go with this. While I could change the code=
 to
> > > > match what you described, I realized with the two files approach th=
ere's
> > > > no need to do even review/lseek() call during the measurement. It m=
ight
> > > > not be very significant compared with the open that was there initi=
ally
> > > > but it's still extra.
> > >=20
> > > We are discussing the resctrl selftests that will accompany the resct=
rl
> > > filesystem in the kernel. When in doubt on how to interact with resct=
rl
> > > users
> > > use the selftests as reference. Needing to open and close a resctrl f=
ile
> > > every time a value needs to be read from it is not the correct guidan=
ce.
> >=20
> > That's actually a different goal from the earlier, but I've no problem
> > adjusting to it.
> >=20
> > Initially, this open/close() refactoring was made because of another go=
al
> > which was to avoid doing extra syscalls during the test.
> >=20
>=20
> It is not clear what you hint at here. Reading twice from an open file
> should not be a huge adjustment so it is not clear to me how this results
> in a big change to this work. As I understand this does match with origin=
al
> goal
> of reducing syscalls since the file need not be opened and closed twice.

What I tried to say is that with a single file, the test uses rewind()=20
that also needs to do a syscall within the test period, whereas if the=20
file is opened twice in advance rewind() won't be needed.

But I've converted it into single file for the sake of serving as an=20
example for other resctrl users.

--=20
 i.
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