linux-kernel - Re: [PATCH v4 02/16] selftests/resctrl: Calculate resctrl FS derived mem bw over sleep(1) only

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Date: Thu, 30 May 2024 08:08:52 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.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>, LKML <linux-kernel@...r.kernel.org>,
	Fenghua Yu <fenghua.yu@...el.com>, Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v4 02/16] selftests/resctrl: Calculate resctrl FS derived
 mem bw over sleep(1) only

Hi Ilpo,

On 5/30/24 4:11 AM, Ilpo Järvinen wrote:
> On Tue, 28 May 2024, Reinette Chatre wrote:
>> On 5/28/24 3:19 AM, Ilpo Järvinen wrote:
>>> On Fri, 24 May 2024, Ilpo Järvinen wrote:
>>>> On Fri, 24 May 2024, Reinette Chatre wrote:
>>>>> On 5/24/24 12:57 AM, Ilpo Järvinen wrote:
>>>>>> On Thu, 23 May 2024, Reinette Chatre wrote:

..

>>>>> It is not necessary to open and close the file every time a value needs
>>>>> to be read from it.
>>>
>>> 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 there's
>>> no need to do even review/lseek() call during the measurement. It might
>>> not be very significant compared with the open that was there initially
>>> but it's still extra.
>>
>> We are discussing the resctrl selftests that will accompany the resctrl
>> filesystem in the kernel. When in doubt on how to interact with resctrl users
>> use the selftests as reference. Needing to open and close a resctrl file
>> every time a value needs to be read from it is not the correct guidance.
> 
> That's actually a different goal from the earlier, but I've no problem
> adjusting to it.
> 
> Initially, this open/close() refactoring was made because of another goal
> which was to avoid doing extra syscalls during the test.
> 

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 original goal
of reducing syscalls since the file need not be opened and closed twice.

Reinette