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Subject: Re: [Linuxarm] Re: [RFC PATCH v4 3/3] scheduler: Add cluster
 scheduler level for x86
To:     "Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>,
        Peter Zijlstra <peterz@infradead.org>
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From:   Tim Chen <tim.c.chen@linux.intel.com>
Message-ID: <e23d04d3-723e-5733-a43a-601f58ecfee4@linux.intel.com>
Date:   Mon, 15 Mar 2021 13:53:38 -0700
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> It seems sensible the more CPU we get in the cluster, the more
> we need the kernel to be aware of its existence.
> 
> Tim, it is possible for you to bring up the cpu_cluster_mask and
> cluster_sibling for x86 so that the topology can be represented
> in sysfs and be used by scheduler? It seems your patch lacks this
> part.

You mean having something in /sys/devices/system/cpu/cpu0/topology
on cluster information so that an external program can 
affinitize to a cluster if it prefers to do so?

Tim  

> 
> BTW, I wonder if x86 can do some improvement on your KMP_AFFINITY
> by leveraging the cluster topology level.
> https://software.intel.com/content/www/us/en/develop/documentation/cpp-compiler-developer-guide-and-reference/top/optimization-and-programming-guide/openmp-support/openmp-library-support/thread-affinity-interface-linux-and-windows.html
> 
> KMP_AFFINITY has thread affinity modes like compact and scatter,
> it seems this "compact" and "scatter" can also use the cluster
> information as you see we are also struggling with the "compact"
> and "scatter" issues here in this patchset :-)
> 
> Thanks
> Barry
>