Hi, I have a simple question, that''s maybe an FAQ: The XEN hypervisor only reports one zonelist during boot, while a normal kernel will report two for a two-node NUMA machine. Now I''m wondering if I create two VMs with roughly half of the RAM (amount one node has), will XEN be clever or dumb when assigning RAM to those VMs? XEN will be clever if it takes the RAM from one node, preferrably that where the assigned CPU is, and it will be dumb if it assigns just any RAM, causing a slowdown of RAM access. Regards, Ulrich _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
> -----Original Message----- > From: xen-users-bounces@lists.xensource.com > [mailto:xen-users-bounces@lists.xensource.com] On Behalf Of > Ulrich Windl > Sent: 09 October 2006 07:10 > To: xen-users@lists.xensource.com > Subject: [Xen-users] Q: NUMA and XEN > > Hi, > > I have a simple question, that''s maybe an FAQ: The XEN > hypervisor only reports one > zonelist during boot, while a normal kernel will report two > for a two-node NUMA > machine. Now I''m wondering if I create two VMs with roughly > half of the RAM > (amount one node has), will XEN be clever or dumb when > assigning RAM to those VMs?Dumb. There''s no guarantee that any domain will get any particular memory, or even that the memory is contiguous within a lump. Until the actual code to support NUMA is in place, you''re just as well off letting the two DomU''s switch between CPU''s as they like - that will at least average out, rather than being "always bad" (if you''re unlucky). Of course, on a two-node Opteron system, I doubt that you''ll be measuring a huge difference unless you''re running some HPC application - in which case you should consider "not using Xen", as HPC on Xen isn''t the most optimal solution [lots of things are slowed down a little bit by the extra layering - which isn''t exactly great for your average HPC application].> > XEN will be clever if it takes the RAM from one node, > preferrably that where the > assigned CPU is, and it will be dumb if it assigns just any > RAM, causing a > slowdown of RAM access.Since Xen isn''t aware of which RAM belongs to which processor, it will be completely random whether you get "good" or "bad" result. -- Mats> > Regards, > Ulrich > > > _______________________________________________ > Xen-users mailing list > Xen-users@lists.xensource.com > http://lists.xensource.com/xen-users > > >_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Ryan is currently working on NUMA support. He can probably give a better idea of the sort of things we''ll be supporting. Regards, Anthony Liguori Ulrich Windl wrote:> Hi, > > I have a simple question, that''s maybe an FAQ: The XEN hypervisor only reports one > zonelist during boot, while a normal kernel will report two for a two-node NUMA > machine. Now I''m wondering if I create two VMs with roughly half of the RAM > (amount one node has), will XEN be clever or dumb when assigning RAM to those VMs? > > XEN will be clever if it takes the RAM from one node, preferrably that where the > assigned CPU is, and it will be dumb if it assigns just any RAM, causing a > slowdown of RAM access. > > Regards, > Ulrich_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
Ryan is currently working on NUMA support. He can probably give a better idea of the sort of things we''ll be supporting. Regards, Anthony Liguori Ulrich Windl wrote:> Hi, > > I have a simple question, that''s maybe an FAQ: The XEN hypervisor only reports one > zonelist during boot, while a normal kernel will report two for a two-node NUMA > machine. Now I''m wondering if I create two VMs with roughly half of the RAM > (amount one node has), will XEN be clever or dumb when assigning RAM to those VMs? > > XEN will be clever if it takes the RAM from one node, preferrably that where the > assigned CPU is, and it will be dumb if it assigns just any RAM, causing a > slowdown of RAM access. > > Regards, > Ulrich_______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users
* Anthony Liguori <aliguori@us.ibm.com> [2006-10-09 17:59]:> Ryan is currently working on NUMA support. He can probably give a > better idea of the sort of things we''ll be supporting. > > Regards, > > Anthony LiguoriThanks for sending this my way, Anthony.> > Ulrich Windl wrote: > >Hi,Hello.> > > >I have a simple question, that''s maybe an FAQ: The XEN hypervisor only > >reports one zonelist during boot, while a normal kernel will report two > >for a two-node NUMA machine. Now I''m wondering if I create two VMs with > >roughly half of the RAM (amount one node has), will XEN be clever or dumb > >when assigning RAM to those VMs?Currently no. Xen doesn''t have any NUMA support at the moment. I''ve developed NUMA [1]support for Xen and modified its page allocator to provide node local memory for guests. The patchset is awaiting approval from the Xen guys. Hopefully, once 3.0.3 is released and xen-unstable opens back up for new development, the patches will be merged and you will be able to give the patches a test on your NUMA hardware. Thanks for the interest. 1. http://lists.xensource.com/archives/html/xen-devel/2006-09/msg00958.html -- Ryan Harper Software Engineer; Linux Technology Center IBM Corp., Austin, Tx (512) 838-9253 T/L: 678-9253 ryanh@us.ibm.com _______________________________________________ Xen-users mailing list Xen-users@lists.xensource.com http://lists.xensource.com/xen-users