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Re: [libvirt] [PATCH] RPC: Support up to 4096 cpus on the host and 256 in the guest



On 06/03/13 12:32, Daniel P. Berrange wrote:
On Tue, May 28, 2013 at 02:35:50PM +0200, Peter Krempa wrote:
The RPC limits for cpu maps didn't allow to use libvirt on ultra big
boxes. This patch increases size of the limits to support a maximum of
4096 cpus on the host with the built-in maximum of 256 cpus per guest.
The full cpu map of such a system takes 128 kilobytes and the map for
vcpu pinning is 512 bytes long.
---
  src/remote/remote_protocol.x | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/remote/remote_protocol.x b/src/remote/remote_protocol.x
index 1ebbce7..a94e0db 100644
--- a/src/remote/remote_protocol.x
+++ b/src/remote/remote_protocol.x
@@ -82,13 +82,13 @@ const REMOTE_DOMAIN_ID_LIST_MAX = 16384;
  const REMOTE_DOMAIN_NAME_LIST_MAX = 16384;

  /* Upper limit on cpumap (bytes) passed to virDomainPinVcpu. */
-const REMOTE_CPUMAP_MAX = 256;
+const REMOTE_CPUMAP_MAX = 512;

  /* Upper limit on number of info fields returned by virDomainGetVcpus. */
-const REMOTE_VCPUINFO_MAX = 2048;
+const REMOTE_VCPUINFO_MAX = 4096;

  /* Upper limit on cpumaps (bytes) passed to virDomainGetVcpus. */
-const REMOTE_CPUMAPS_MAX = 16384;
+const REMOTE_CPUMAPS_MAX = 131072;

  /* Upper limit on migrate cookie. */
  const REMOTE_MIGRATE_COOKIE_MAX = 16384;

4096 sounds large, but I can't help wondering if we should pre-empt the
inevitable and go even bigger. In terms of RPC message size, we can
afford to allow 16384 host CPUS and 4096 guest CPUS ?

We can do that. The cpu map for a 16384 host with 4096 guest cpus is 8 MiB large. The RPC message limit is almost 16MiB so we should be fine even with those (now seemingly insane) numbers.

I'll send a v2 in a moment.



Daniel


Peter


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