Re: disabling halt polling broken? (was Re: [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a ne
Christian Borntraeger <[email protected]>
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Am 27.09.21 um 17:03 schrieb Paolo Bonzini: > On 27/09/21 16:59, Sean Christopherson wrote: >>> commit acd05785e48c01edb2c4f4d014d28478b5f19fb5 >>> Author: David Matlack<[email protected]> >>> AuthorDate: Fri Apr 17 15:14:46 2020 -0700 >>> Commit: Paolo Bonzini<[email protected]> >>> CommitDate: Fri Apr 24 12:53:17 2020 -0400 >>> >>> kvm: add capability for halt polling >>> >>> broke the possibility for an admin to disable halt polling for already running KVM guests. >>> In past times doing >>> echo 0 > /sys/module/kvm/parameters/halt_poll_ns >>> >>> stopped polling system wide. >>> Now all KVM guests will use the halt_poll_ns value that was active during >>> startup - even those that do not use KVM_CAP_HALT_POLL. >>> >>> I guess this was not intended? > > No, but... > >> I would go so far as to say that halt_poll_ns should be a hard limit on >> the capability > > ... this would not be a good idea I think. Anything that wants to do a lot of polling can just do "for (;;)". > > So I think there are two possibilities that makes sense: > > * track what is using KVM_CAP_HALT_POLL, and make writes to halt_poll_ns follow that what about using halt_poll_ns for those VMs that did not uses KVM_CAP_HALT_POLL and the private number for those that did. > > * just make halt_poll_ns read-only. > > Paolo >