Messages in this thread | | | Date | Tue, 16 Sep 2014 08:44:03 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: Consider multiple nodes in a single socket to be "sane" |
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* Chuck Ebbert <cebbert.lkml@gmail.com> wrote:
> On Tue, 16 Sep 2014 05:29:20 +0200 > Peter Zijlstra <peterz@infradead.org> wrote: > > > On Mon, Sep 15, 2014 at 03:26:41PM -0700, Dave Hansen wrote: > > > > > > I'm getting the spew below when booting with Haswell (Xeon > > > E5-2699) CPUs and the "Cluster-on-Die" (CoD) feature > > > enabled in the BIOS. > > > > What is that cluster-on-die thing? I've heard it before but > > never could find anything on it. > > Each CPU has 2.5MB of L3 connected together in a ring that > makes it all act like a single shared cache. The HW tries to > place the data so it's closest to the CPU that uses it. On the > larger processors there are two rings with an interconnect > between them that adds latency if a cache fetch has to cross > that. CoD breaks that connection and effectively gives you two > nodes on one die.
Note that that's not really a 'NUMA node' in the way lots of places in the kernel assume it: permanent placement assymetry (and access cost assymetry) of RAM.
It's a new topology construct that needs new handling (and probably a new mask): Non Uniform Cache Architecture (NUCA) or so.
Thanks,
Ingo
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