Re: disabling halt polling broken? (was Re: [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a ne
Paolo Bonzini <[email protected]>
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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 * just make halt_poll_ns read-only. Paolo