RE: [Xen-devel] [PATCH] nr_cpus calculation problem due to incorrectsockets_per_node

["Puthiyaparambil, Aravindh" <aravindh.puthiyaparambil@xxxxxxxxxx>]

Beth,

With this patch you are able to come up with 128 logical CPUs on x86_64
Xen? I.E you did a compile with max_phys_cpus=128 and successfully
booted? Don't you need to also increase NR_RESERVED_GDT_PAGES based on
number of CPUs among other things?

Thanks,

Aravindh Puthiyaparambil 
Virtualization Engineer
Virtual Systems Development
Unisys, Tredyffrin PA

-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of beth kon
Sent: Friday, October 19, 2007 10:47 AM
To: Xen-devel@xxxxxxxxxxxxxxxxxxx; xen-ppc-devel@xxxxxxxxxxxxxxxxxxx;
xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] [PATCH] nr_cpus calculation problem due to
incorrectsockets_per_node

Testing on an 8-node 128-way NUMA machine has exposed a problem with 
Xen's nr_cpus calculation. In this case, since Xen cuts off recognized 
CPUs at 32, the machine appears to have 16 CPUs on the first and second 
nodes and none on the remaining nodes. Given this asymmetry, the 
calculation of sockets_per_node (which is later used to calculate 
nr_cpus) is incorrect:

pi->sockets_per_node = num_online_cpus() /(num_online_nodes() * 
pi->cores_per_socket * pi->threads_per_core);

The most straightforward solution is to remove sockets_per_node, and 
instead determine nr_cpus directly from num_online_cpus.

This patch has been tested on x86_64 NUMA machines.

-- 
Elizabeth Kon (Beth)
IBM Linux Technology Center
Open Hypervisor Team
email: eak@xxxxxxxxxx


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