linux-kernel - RE: [PATCH v5 0/6] Add hardware prefetch control driver for A64FX and x86

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Message-ID: <OSBPR01MB203739DD69FB8C50990C356A80B89@OSBPR01MB2037.jpnprd01.prod.outlook.com>
Date:   Tue, 28 Jun 2022 13:55:11 +0000
From:   "tarumizu.kohei@...itsu.com" <tarumizu.kohei@...itsu.com>
To:     'Linus Walleij' <linus.walleij@...aro.org>
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Subject: RE: [PATCH v5 0/6] Add hardware prefetch control driver for A64FX and
 x86

Hi Linus,

> The right way to solve this is to make the Linux kernel contain the necessary
> heuristics to identify which tasks and thus cores need this to improve efficiency
> and then apply it automatically.
> 
> Putting it in userspace is making a human do a machines job which isn't
> sustainable.
> 
> By putting the heuristics in kernelspace Linux will improve performance also on
> workloads the human operator didn't think of as the machine will detect them from
> statictical or other behaviour patterns.

In order to put the heuristics into kernelspace Linux, I think it
necessary to consider the following two points.

1) Which cores are tied with the process?
This is different from the core on which the process can run. It
probably need to combine some CPU resource limit to avoid affecting
non-target processes.

2) How to derive the value to set in the register?
It is necessary to verify whether an appropriate set value can be
derived using statistical information, etc. In addition, to prevent
the cost of automatic derivation from exceeding the value that would
be improved by it.

I don't have a prospect for resolving these issues yet. I will
continue these considerations.