From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH RFC] kvm: x86: add halt_poll module parameter Date: Thu, 05 Feb 2015 20:20:54 +0100 Message-ID: <54D3C296.7030207@redhat.com> References: <1423152325-5094-1-git-send-email-pbonzini@redhat.com> <54D3BC94.9010007@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Cc: riel@redhat.com, rkrcmar@redhat.com, mtosatti@redhat.com To: Jan Kiszka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <54D3BC94.9010007@siemens.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/02/2015 19:55, Jan Kiszka wrote: > > This patch introduces a new module parameter for the KVM module; when it > > is present, KVM attempts a bit of polling on every HLT before scheduling > > itself out via kvm_vcpu_block. > > Wouldn't it be better to tune this on a per-VM basis? Think of mixed > workloads with some latency-sensitive and some standard VMs. Yes, but: 1) this turned out to be very cheap, so a per-host tunable is not too bad; 2) it also affects only very few workloads (for example network workloads can already do polling in the guest) so it only affects few people; 3) long term anyway we want it to auto tune, which is better than tuning it per-VM. Paolo