From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752791AbbIOQow (ORCPT ); Tue, 15 Sep 2015 12:44:52 -0400 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:43396 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751810AbbIOQou (ORCPT ); Tue, 15 Sep 2015 12:44:50 -0400 X-Helo: d06dlp03.portsmouth.uk.ibm.com X-MailFrom: cornelia.huck@de.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Date: Tue, 15 Sep 2015 18:44:44 +0200 From: Cornelia Huck To: Paolo Bonzini Cc: Jason Wang , gleb@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com Subject: Re: [PATCH V6 6/6] kvm: add fast mmio capabilitiy Message-ID: <20150915184444.6cc6e648.cornelia.huck@de.ibm.com> In-Reply-To: <55F8477D.7040803@redhat.com> References: <1442299319-5253-1-git-send-email-jasowang@redhat.com> <1442299319-5253-7-git-send-email-jasowang@redhat.com> <55F8344B.50300@redhat.com> <20150915181319.097e341c.cornelia.huck@de.ibm.com> <55F8477D.7040803@redhat.com> Organization: IBM Deutschland Research & Development GmbH Vorsitzende des Aufsichtsrats: Martina Koederitz =?UTF-8?B?R2VzY2jDpGZ0c2bDvGhydW5nOg==?= Dirk Wittkopp Sitz der Gesellschaft: =?UTF-8?B?QsO2Ymxpbmdlbg==?= Registergericht: Amtsgericht Stuttgart, HRB 243294 X-Mailer: Claws Mail 3.8.0 (GTK+ 2.24.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15091516-0025-0000-0000-000006DE56BC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 15 Sep 2015 18:29:49 +0200 Paolo Bonzini wrote: > On 15/09/2015 18:13, Cornelia Huck wrote: > > On Tue, 15 Sep 2015 17:07:55 +0200 > > Paolo Bonzini wrote: > > > >> On 15/09/2015 08:41, Jason Wang wrote: > >>> +With KVM_CAP_FAST_MMIO, a zero length mmio eventfd is allowed for > >>> +kernel to ignore the length of guest write and get a possible faster > >>> +response. Note the speedup may only work on some specific > >>> +architectures and setups. Otherwise, it's as fast as wildcard mmio > >>> +eventfd. > >> > >> I don't really like tying the capability to MMIO, especially since > >> zero length ioeventfd is already accepted for virtio-ccw. > > > > Actually, zero length ioeventfd does not make sense for virtio-ccw; > > Can you explain why? If there is any non-zero valid length, "wildcard > length" (represented by zero) would also make sense. What is a wildcard match supposed to mean in this case? The datamatch field contains the queue index for the device specified in the address field. The hypercall interface associated with the eventfd always has device + queue index in its parameters; there is no interface for "notify device with all its queues". But maybe I'm just lacking imagination :)