From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [GIT PULL] First batch of KVM changes for 4.1 Date: Fri, 17 Apr 2015 15:43:35 +0200 Message-ID: <20150417134335.GI23123@twins.programming.kicks-ass.net> References: <1428678089-16291-1-git-send-email-pbonzini@redhat.com> <20150417085238.GJ17717@twins.programming.kicks-ass.net> <20150417091745.GA24151@twins.programming.kicks-ass.net> <5530DBED.5080508@redhat.com> <20150417103654.GE5029@twins.programming.kicks-ass.net> <5530E28F.2030401@redhat.com> <20150417105506.GF5029@twins.programming.kicks-ass.net> <553100C1.5000408@redhat.com> <20150417131037.GG23123@twins.programming.kicks-ass.net> <55310CF2.6070107@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, gleb@kernel.org, kvm@vger.kernel.org, Ralf Baechle , mtosatti@redhat.com, luto@kernel.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <55310CF2.6070107@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Fri, Apr 17, 2015 at 03:38:58PM +0200, Paolo Bonzini wrote: > > The path this notifier is called from has nothing to do with those > > costs. > > How not? The task is going to incur those costs, it's not like half > a dozen extra instruction make any difference. But anyway... Its attributed to the entity doing the migration, which can be the wakeup path or a softirq. And we very much do care about the wakeup path. > ... that's a valid objection. Please look at the patch below. Still a NAK on that, distros have no choice but to enable that CONFIG option because people might want to run KVM. CONFIG options are pointless if they end up being mandatory.