On Wed, 16 Dec 2015 18:22:20 +0100 Igor Mammedov <imamm...@redhat.com> wrote:
> On Wed, 16 Dec 2015 16:57:54 +0100 > Andreas Färber <afaer...@suse.de> wrote: [...] > > > > Attendees in Seattle said that thread-level hot-plug were dangerous > > for Linux guests due to assumptions in the (guest's) scheduler > > breaking for any incompletely filled cores or sockets. No one > > present > There is not such thing as cpu hotplug at socket level in x86 linux > so far. CPUs are plugged at logical(thread) cpu level, one at a time. > And ACPI spec does the same (describes logical CPUs) and hotplug > notification in guest handled per one logical cpu at a time. BTW: from my experience with CPU hotplug, I've had to fix only one topology+sched related bug in kernel but more bugs were related to fast CPU online/offline especially if host is over-committed. And plugging whole socket would lead to a rapid sequence of hotplugging CPUs which has been causing non deterministic kernel crash/lock up much more often than topology issues, there are still bugs to fix in that area.
