On Tue, Mar 22, 2016 at 09:14:33AM +0100, Manuel Bouyer wrote: > On Mon, Mar 21, 2016 at 07:10:51PM -0400, Thor Lancelot Simon wrote: > > > What's particularly curious here to me is that we are seeing > > twice as many interrupts as we should, in the poorly performing Xen > > case. > > What controller is it ? maybe when running faster it's able > to coalesce some interrupts ? > The irq rate seems to be mostly the same in both cases, but with the > number of I/O ops cut by half in the Xen case.
The controller is a ciss. I observed the same problems with an arcmsr. I don't think this has anything to do with the controller. At 1/2 the data and request rate, under Xen we use 60% CPU as interrupt time while with a native kernel, it's 1-3%. The same test's easy to reproduce with any Xen dom0, since all you have to do is dd from the raw disk into /dev/null. Do you see >40% interrupt time and all your idle CPU go away? That's the issue. Thor
