Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752548AbZKKJYX (ORCPT ); Wed, 11 Nov 2009 04:24:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752228AbZKKJYW (ORCPT ); Wed, 11 Nov 2009 04:24:22 -0500 Received: from mail2.shareable.org ([80.68.89.115]:34286 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752202AbZKKJYV (ORCPT ); Wed, 11 Nov 2009 04:24:21 -0500 Date: Wed, 11 Nov 2009 09:24:09 +0000 From: Jamie Lokier To: Anthony Liguori Cc: Avi Kivity , agl@linux.vnet.ibm.com, Rusty Russell , qemu-devel@nongnu.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [Qemu-devel] Re: virtio: Add memory statistics reporting to the balloon driver Message-ID: <20091111092409.GA24646@shareable.org> References: <1257782838.2835.5.camel@aglitke> <1257784326.2835.16.camel@aglitke> <200911101312.02650.rusty@rustcorp.com.au> <4AF97A5E.1070801@codemonkey.ws> <4AF97C1A.2080609@redhat.com> <4AF97F93.2080707@us.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AF97F93.2080707@us.ibm.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1482 Lines: 36 Anthony Liguori wrote: > Avi Kivity wrote: > >On 11/10/2009 04:36 PM, Anthony Liguori wrote: > >> > >>>A stats vq might solve this more cleanly? > >> > >>actual and target are both really just stats. Had we implemented > >>those with a vq, I'd be inclined to agree with you but since they're > >>implemented in the config space, it seems natural to extend the > >>config space with other stats. > >> > > > >There is in fact a difference; actual and target are very rarely > >updated, while the stats are updated very often. Using a vq means a > >constant number of exits per batch instead of one exit per statistic. > >If the vq is host-driven, it also allows the host to control the > >update frequency dynamically (i.e. stop polling when there is no > >memory pressure). > > I'm not terribly opposed to using a vq for this. I would expect the > stat update interval to be rather long (10s probably) but a vq works > just as well. If there's no memory pressure and no guest activity, you probably want the stat update to be as rare as possible to avoid wakeups. Save power on laptops, that sort of thing. If there's a host user interested in the state ("qemutop?"), you may want updates more often than 10s. -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/