From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 02/26] KVM: PPC: Convert MSR to shared page Date: Sun, 27 Jun 2010 12:50:29 +0300 Message-ID: <4C271EE5.1060401@redhat.com> References: <1277508314-915-1-git-send-email-agraf@suse.de> <1277508314-915-3-git-send-email-agraf@suse.de> <4C2708EB.9020500@redhat.com> <651805F1-54AB-466F-8D23-D053D8082177@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "kvm-ppc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , KVM list , linuxppc-dev To: Alexander Graf Return-path: In-Reply-To: <651805F1-54AB-466F-8D23-D053D8082177-l3A5Bk7waGM@public.gmane.org> Sender: kvm-ppc-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: kvm.vger.kernel.org On 06/27/2010 12:38 PM, Alexander Graf wrote: > > Am 27.06.2010 um 10:16 schrieb Avi Kivity : > >> On 06/26/2010 02:24 AM, Alexander Graf wrote: >>> One of the most obvious registers to share with the guest directly >>> is the >>> MSR. The MSR contains the "interrupts enabled" flag which the guest >>> has to >>> toggle in critical sections. >>> >>> So in order to bring the overhead of interrupt en- and disabling >>> down, let's >>> put msr into the shared page. Keep in mind that even though you can >>> fully read >>> its contents, writing to it doesn't always update all state. There >>> are a few >>> safe fields that don't require hypervisor interaction. See the guest >>> implementation that follows later for reference. >>> >> >> >> You mean, see the documentation for reference. >> >> It should be possible to write the guest code looking only at the >> documentation. > > *shrug* since we're writing open source I don't mind telling people to > read code for a reference implemenration. It's impossible to infer from the source what's a guaranteed part of the interface and what is just an implementation artifact. So people rely on implementation artifacts (or even bugs) and that reduces our ability to change things. > If well written, that's more comprehensible than documentation anyways > :). If the documentation is poorly written, yes. -- error compiling committee.c: too many arguments to function