Messages in this thread | | | Date | Tue, 5 May 2009 11:22:38 +0200 | From | Andreas Herrmann <> | Subject | Re: [PATCH 0/3] x86: adapt CPU topology detection for AMD Magny-Cours |
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On Mon, May 04, 2009 at 10:16:15PM +0200, Andi Kleen wrote: > Andreas Herrmann <andreas.herrmann3@amd.com> writes: > > > Following patches add support for AMD Magny-Cours CPU. > > > > I slightly change struct cpuinfo where I'd like to introduce > > cpu_node_id to reflect CPU topology for AMD Magny-Cours CPU which > > consists of two internal-nodes. > > It's unclear to me why you need this special case versus > just using the normal NUMA distances to represent the internal > nodes as "nearby nodes" versus sockets as "farer away".
NUMA memory allocation and scheduling based on SRAT works just fine w/o that fix. But the patches are _not_ for NUMA node detection.
This is for CPU topology detection -- which cores are using the same northbridge.
> Essentially it should be just two level NUMA which can be already > described fine for the scheduler or VM using the existing SRAT > mechanism.
It doesn't suffice to rely on SRAT here.
Best example is node interleaving. Usually you won't get a SRAT table on such a system. Thus you see just one NUMA node in /sys/devices/system/node. But on such a configuration you still see (and you want to see) the correct CPU topology information in /sys/devices/system/cpu/cpuX/topology. Based on that you always can figure out which cores are on the same physical package independent of availability and contents of SRAT and even with kernels that are compiled w/o NUMA support.
A big change with Magny-Cours in contrast to other AMD CPUs is that instead of
physical package == one northbridge (one node)
we have
physical package == two northbridges (two nodes)
and this needs to be represented somehow in the kernel.
> Who needs this additional information?
The kernel needs to know this when accessing processor configuration space, when accessing shared MSRs or for counting northbridge specific events.
Regards, Andreas
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