From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753969AbZKBHHV (ORCPT ); Mon, 2 Nov 2009 02:07:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752895AbZKBHHU (ORCPT ); Mon, 2 Nov 2009 02:07:20 -0500 Received: from mx1.redhat.com ([209.132.183.28]:62673 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752960AbZKBHHT (ORCPT ); Mon, 2 Nov 2009 02:07:19 -0500 Date: Mon, 2 Nov 2009 09:07:20 +0200 From: Gleb Natapov To: Rik van Riel Cc: kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 01/11] Add shared memory hypercall to PV Linux guest. Message-ID: <20091102070720.GF29477@redhat.com> References: <1257076590-29559-1-git-send-email-gleb@redhat.com> <1257076590-29559-2-git-send-email-gleb@redhat.com> <4AEE5FA3.1020104@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AEE5FA3.1020104@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 01, 2009 at 11:27:15PM -0500, Rik van Riel wrote: > On 11/01/2009 06:56 AM, Gleb Natapov wrote: > >Add hypercall that allows guest and host to setup per cpu shared > >memory. > > While it is pretty obvious that we should implement > the asynchronous pagefaults for KVM, so a swap-in > of a page the host swapped out does not stall the > entire virtual CPU, I believe that adding extra > data accesses at context switch time may not be > the best tradeoff. > > It may be better to simply tell the guest what > address is faulting (or give the guest some other > random unique number as a token). Then, once the > host brings that page into memory, we can send a > signal to the guest with that same token. > > The problem of finding the task(s) associated with > that token can be left to the guest. A little more > complexity on the guest side, but probably worth it > if we can avoid adding cost to the context switch > path. > This is precisely what this series implements. The function below is leftover from previous implementation, not used by the rest of the patch and removed by a later patch. Just a left over from rebase. Sorry about that. Will be fixed for future submissions. > >+static void kvm_end_context_switch(struct task_struct *next) > >+{ > >+ struct kvm_vcpu_pv_shm *pv_shm = > >+ per_cpu(kvm_vcpu_pv_shm, smp_processor_id()); > >+ > >+ if (!pv_shm) > >+ return; > >+ > >+ pv_shm->current_task = (u64)next; > >+} > >+ > > > > -- > All rights reversed. -- Gleb.