Xen (and others Hypervisors) how do they handle IPIs?
If CPUs are mapped around, how are IPIs handled? I assume they must be emulated? I've noticed that under Xen (on both Amazon EC2 and a Redhat server) whenever you schedule a thread it always sits on the run queue for 20 uSecs before it starts running. It looks to me like it's the IPI taking a long time to be emulated. We have some workloads where there is a lot of flipping back and forth between threads and they are slowed down by an order of magnitude due to this.. turning off NOADAPTIVE(mumble) seems to help a bit as some of the reschedules go away, but it's still a problem. Does anyone know if BHyVe or HyperV also have this problem? I have not yet gone to the source of Xen to see what it does but it would be educational to know what the other Hypervisors do. ___ freebsd-virtualization@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-virtualization To unsubscribe, send any mail to freebsd-virtualization-unsubscr...@freebsd.org
Re: Xen (and others Hypervisors) how do they handle IPIs?
On 25/09/13 16:56, Julian Elischer wrote: If CPUs are mapped around, how are IPIs handled? I assume they must be emulated? I've noticed that under Xen (on both Amazon EC2 and a Redhat server) whenever you schedule a thread it always sits on the run queue for 20 uSecs before it starts running. It looks to me like it's the IPI taking a long time to be emulated. This has been improved on the FreeBSD Xen PVHVM port by using PV IPIs instead of the emulated ones, see r255331. It should be faster than the previous emulated implementation. ___ freebsd-virtualization@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-virtualization To unsubscribe, send any mail to freebsd-virtualization-unsubscr...@freebsd.org
