> From: Stephen Hemminger [mailto:step...@networkplumber.org] > Sent: Sunday, November 27, 2016 01:06 > To: Vitaly Kuznetsov <vkuzn...@redhat.com> > Cc: de...@linuxdriverproject.org; linux-kernel@vger.kernel.org; KY Srinivasan > <k...@microsoft.com>; Haiyang Zhang <haiya...@microsoft.com>; Dexuan Cui > <de...@microsoft.com> > Subject: Re: [PATCH 0/7] hv: CPU onlining/offlining fixes and improvements > > On Fri, 25 Nov 2016 13:48:36 +0100 > Vitaly Kuznetsov <vkuzn...@redhat.com> wrote: > > > Some time ago we forbade CPU offlining for Hyper-V and this was sufficient > > if you boot with all CPUs onlined. Turns out, people may want to limit the > > number online CPUs by passing 'maxcpus=' kernel parameter and we hit a > > crash in Hyper-V code in this case. After some thinking, I think we may not > > only fix the crash but also make the offlining prevention fine-grained: we > > need to prevent from offlining CPUs which have VMBus channels attached > > only. All offlined CPUs may always be onlined. > > > > As a temporary solution this is ok, but long term we need to support > dynamic CPU online/offline.
If a CPU is bound to some channels, it seems impossible to make it offline, unless Hyper-V supplies a mechanism to dynamically rebind the channels (i.e. without closing & opening the channels) to another CPU, e.g. CPU0. Currently it looks there is no such mechanism. For CPU online, my understanding is: this patchset of Vitaly actually makes it work (see PATCH 6/7). Thanks, -- Dexuan
