From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756113Ab2BGMEG (ORCPT ); Tue, 7 Feb 2012 07:04:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:49286 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755769Ab2BGMEF (ORCPT ); Tue, 7 Feb 2012 07:04:05 -0500 Message-ID: <4F31132F.3010100@redhat.com> Date: Tue, 07 Feb 2012 14:03:59 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0) Gecko/20120131 Thunderbird/10.0 MIME-Version: 1.0 To: Anthony Liguori CC: Rob Earhart , linux-kernel , KVM list , qemu-devel Subject: Re: [Qemu-devel] [RFC] Next gen kvm api References: <4F2AB552.2070909@redhat.com> <4F2E80A7.5040908@redhat.com> <4F3025FB.1070802@codemonkey.ws> In-Reply-To: <4F3025FB.1070802@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/06/2012 09:11 PM, Anthony Liguori wrote: > > I'm not so sure. ioeventfds and a future mmio-over-socketpair have to > put the kthread to sleep while it waits for the other end to process > it. This is effectively equivalent to a heavy weight exit. The > difference in cost is dropping to userspace which is really neglible > these days (< 100 cycles). On what machine did you measure these wonderful numbers? But I agree a heavyweight exit is probably faster than a double context switch on a remote core. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.