[Openmp-dev] cpuinfo file reliance

[Churbanov, Andrey via Openmp-dev]

The cpuinfo file topology method was designed to show the library machine topology without requiring it to investigate the topology itself.
The file can be written manually, it should not necessarily be /proc/cpuinfo.  It can be /my_folder/my_cpuinfo_file for example, or c:\my_folder\my_cpuinfo_file.txt on Windows.
Only requirement is to follow format that the library can recognize.  One can always write own file, e.g. basing on info provided by lscpu or any other tool.

This method can work on any architecture that allows to bind a thread using an affinity mask.

The goal was to allow to test affinity on machines where cpuid instruction cannot work, or cpuid has interface that the library cannot recognize, or to test binding on some future architecture using old system, or to avoid issuing cupid instruction by the library for some reason, etc.

-- Andrey

From: Openmp-dev <openmp-dev-bounces at lists.llvm.org> On Behalf Of Hal Finkel via Openmp-dev
Sent: Saturday, July 4, 2020 12:18 AM
To: Itaru Kitayama <itaru.kitayama at gmail.com>; Jeff Hammond <jeff.science at gmail.com>
Cc: openmp-dev <openmp-dev at lists.llvm.org>
Subject: Re: [Openmp-dev] cpuinfo file reliance



On 7/3/20 3:42 PM, Itaru Kitayama via Openmp-dev wrote:
Jeff,
Linux supports other arches than X86, and the
layout of cpuinfo is different across the architectures.

In the runtime code if you take a look at already  there are ifdefs.

Itaru.



The alternative that you're proposing is to fork lscpu to read /proc/cpuinfo instead?

We do understand that /proc/cpuinfo has architecture dependencies, and this is unfortunate in this context, but it is the interface that Linux provides. How does lscpu deal with those dependencies? Should our parser just be more robust?

 -Hal



On Fri, Jul 3, 2020 at 23:48 Jeff Hammond <jeff.science at gmail.com<mailto:jeff.science at gmail.com>> wrote:
I’m not sure lscpu program is any better and it’s not standard on Linux the way /proc/cpuinfo is.

What is the specific problem you are seeing? Perhaps you can explain that before trying to design a solution.

Jeff

> On Jul 2, 2020, at 10:55 PM, Itaru Kitayama via Openmp-dev <openmp-dev at lists.llvm.org<mailto:openmp-dev at lists.llvm.org>> wrote:
>
> Is there a plan to move away from arch dependent cpuinfo file to lscup
> when creating an affinity map? It has clearly different a format on AArch64.
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--

Hal Finkel

Lead, Compiler Technology and Programming Languages

Leadership Computing Facility

Argonne National Laboratory

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