linux-kernel - Re: [RFC][PATCH 2/6] x86: introduce cpumask specifically for the package

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Date:	Thu, 18 Sep 2014 16:57:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dave Hansen <dave@...1.net>
Cc:	mingo@...nel.org, hpa@...ux.intel.com, brice.goglin@...il.com,
	bp@...en8.de, linux-kernel@...r.kernel.org,
	dave.hansen@...ux.intel.com
Subject: Re: [RFC][PATCH 2/6] x86: introduce cpumask specifically for the
 package

On Wed, Sep 17, 2014 at 03:33:14PM -0700, Dave Hansen wrote:
> 
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> As noted by multiple reports:
> 
> 	https://lkml.org/lkml/2014/9/15/1240
> 	https://lkml.org/lkml/2014/7/28/442
> 
> the sched domains code has some assumptions that break on newer
> AMD and Intel CPUs.  Namely, the code assumes that NUMA node
> boundaries always lie outside of a CPU package.  That assumption
> is no longer true with Intel's Cluster-on-Die found in Haswell
> CPUs (with a special BIOS config knob) and AMD's DCM feature.
> 
> Essentially, the 'cpu_core_map' is no longer suitable for
> enumerating all the CPUs in a physical package.
> 
> This patch introduces a new map which is specifically built by
> consulting the the physical package ids instead of inferring the
> information from NUMA nodes.
> 
> This still leaves us with a broken 'core_siblings_list' in sysfs,
> but a later patch will fix that up too.

If we do dynamic topology layout we don't need a second mask I think.
The machines that have multiple packages per node will simply present a
different sched_domain_topology than the machines that have multiple
nodes per package.

Specifically, in the former we include the package_mask as DIE level, in
the other case we leave it out entirely and rely on the SLIT table to
build the right domain topology.
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