2017-08-15 11:00+0800, Lan Tianyu: > On 2017年08月12日 03:35, Konrad Rzeszutek Wilk wrote: >> On Fri, Aug 11, 2017 at 03:00:20PM +0200, Radim Krčmář wrote: >>> 2017-08-11 10:11+0200, David Hildenbrand: >>>> On 11.08.2017 09:49, Lan Tianyu wrote: >>>>> On 2017年08月11日 01:50, Konrad Rzeszutek Wilk wrote: >>>>>> Are there any issues with increasing the value from 288 to 352 right now? >>>>> >>>>> No found. >>> >>> Yeah, the only issue until around 2^20 (when we reach the maximum of >>> logical x2APIC addressing) should be the size of per-VM arrays when only >>> few VCPUs are going to be used. (I was talking only about the KVM side.) >> Migration with 352 CPUs all being busy dirtying memory and also poking >> at various I/O ports (say all of them dirtying the VGA) is no problem? > > This depends on what kind of workload is running during migration. I > think this may affect service down time since there maybe a lot of dirty > memory data to transfer after stopping vcpus. This also depends on how > user sets "migrate_set_downtime" for qemu. But I think increasing vcpus > will break migration function. Utilizing post-copy in the last migration phase should make migration of busy big guests possible. (I agree that pre-copy in not going to be feasible.)
