linux-kernel - RE: [RFC PATCH v5 1/4] topology: Represent clusters of CPUs within a die

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Date:   Fri, 19 Mar 2021 06:57:08 +0000
From:   "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
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Subject: RE: [RFC PATCH v5 1/4] topology: Represent clusters of CPUs within a
 die



> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Friday, March 19, 2021 7:35 PM
> To: Song Bao Hua (Barry Song) <song.bao.hua@...ilicon.com>
> Cc: tim.c.chen@...ux.intel.com; catalin.marinas@....com; will@...nel.org;
> rjw@...ysocki.net; vincent.guittot@...aro.org; bp@...en8.de;
> tglx@...utronix.de; mingo@...hat.com; lenb@...nel.org; peterz@...radead.org;
> dietmar.eggemann@....com; rostedt@...dmis.org; bsegall@...gle.com;
> mgorman@...e.de; msys.mizuma@...il.com; valentin.schneider@....com; Jonathan
> Cameron <jonathan.cameron@...wei.com>; juri.lelli@...hat.com;
> mark.rutland@....com; sudeep.holla@....com; aubrey.li@...ux.intel.com;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
> linux-acpi@...r.kernel.org; x86@...nel.org; xuwei (O) <xuwei5@...wei.com>;
> Zengtao (B) <prime.zeng@...ilicon.com>; guodong.xu@...aro.org; yangyicong
> <yangyicong@...wei.com>; Liguozhu (Kenneth) <liguozhu@...ilicon.com>;
> linuxarm@...neuler.org; hpa@...or.com
> Subject: Re: [RFC PATCH v5 1/4] topology: Represent clusters of CPUs within
> a die
> 
> On Fri, Mar 19, 2021 at 05:16:15PM +1300, Barry Song wrote:
> > diff --git a/Documentation/admin-guide/cputopology.rst
> b/Documentation/admin-guide/cputopology.rst
> > index b90dafc..f9d3745 100644
> > --- a/Documentation/admin-guide/cputopology.rst
> > +++ b/Documentation/admin-guide/cputopology.rst
> > @@ -24,6 +24,12 @@ core_id:
> >  	identifier (rather than the kernel's).  The actual value is
> >  	architecture and platform dependent.
> >
> > +cluster_id:
> > +
> > +	the Cluster ID of cpuX.  Typically it is the hardware platform's
> > +	identifier (rather than the kernel's).  The actual value is
> > +	architecture and platform dependent.
> > +
> >  book_id:
> >
> >  	the book ID of cpuX. Typically it is the hardware platform's
> > @@ -56,6 +62,14 @@ package_cpus_list:
> >  	human-readable list of CPUs sharing the same physical_package_id.
> >  	(deprecated name: "core_siblings_list")
> >
> > +cluster_cpus:
> > +
> > +	internal kernel map of CPUs within the same cluster.
> > +
> > +cluster_cpus_list:
> > +
> > +	human-readable list of CPUs within the same cluster.
> > +
> >  die_cpus:
> >
> >  	internal kernel map of CPUs within the same die.
> 
> Why are these sysfs files in this file, and not in a Documentation/ABI/
> file which can be correctly parsed and shown to userspace?

Well. Those ABIs have been there for much a long time. It is like:

[root@...h1 topology]# ls
core_id  core_siblings  core_siblings_list  physical_package_id thread_siblings  thread_siblings_list
[root@...h1 topology]# pwd
/sys/devices/system/cpu/cpu100/topology
[root@...h1 topology]# cat core_siblings_list
64-127
[root@...h1 topology]#

> 
> Any chance you can fix that up here as well?

Yes. we will send a separate patch to address this, which won't
be in this patchset. This patchset will base on that one.

> 
> Also note that "list" is not something that goes in sysfs, sysfs is "one
> value per file", and a list is not "one value".  How do you prevent
> overflowing the buffer of the sysfs file if you have a "list"?
> 

At a glance, the list is using "-" rather than a real list
[root@...h1 topology]# cat core_siblings_list
64-127

Anyway, I will take a look if it has any chance to overflow.

> thanks,
> 
> greg k-h

Thanks
Barry