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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id r23sm20063784pjo.3.2021.09.27.08.15.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Sep 2021 08:15:57 -0700 (PDT) Date: Mon, 27 Sep 2021 15:15:53 +0000 From: Sean Christopherson To: Paolo Bonzini Subject: Re: disabling halt polling broken? (was Re: [PATCH 00/14] KVM: Halt-polling fixes, cleanups and a new stat) Message-ID: References: <20210925005528.1145584-1-seanjc@google.com> <03f2f5ab-e809-2ba5-bd98-3393c3b843d2@de.ibm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: Cc: Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-kernel@vger.kernel.org, Paul Mackerras , Claudio Imbrenda , kvmarm@lists.cs.columbia.edu, Janosch Frank , Marc Zyngier , Joerg Roedel , Huacai Chen , Christian Borntraeger , Aleksandar Markovic , Jon Cargille , kvm-ppc@vger.kernel.org, David Matlack , linux-arm-kernel@lists.infradead.org, Jim Mattson , Cornelia Huck , linux-mips@vger.kernel.org, Vitaly Kuznetsov X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Mon, Sep 27, 2021, Paolo Bonzini wrote: > On 27/09/21 16:59, Sean Christopherson wrote: > > > commit acd05785e48c01edb2c4f4d014d28478b5f19fb5 > > > Author: David Matlack > > > AuthorDate: Fri Apr 17 15:14:46 2020 -0700 > > > Commit: Paolo Bonzini > > > 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 (;;)". Hmm, true, there is no danger to the system in having the capability override the module param. > 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 I think this option makes more sense, making halt_poll_ns read-only is basically forcing users to switch to KVM_CAP_HALT_POLL. > * just make halt_poll_ns read-only. > > Paolo > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm