From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38679) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aYaTQ-0005RX-K2 for qemu-devel@nongnu.org; Wed, 24 Feb 2016 09:31:29 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aYaTM-0000OP-Ht for qemu-devel@nongnu.org; Wed, 24 Feb 2016 09:31:28 -0500 Received: from mx1.redhat.com ([209.132.183.28]:60633) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aYaTM-0000O7-AV for qemu-devel@nongnu.org; Wed, 24 Feb 2016 09:31:24 -0500 Date: Wed, 24 Feb 2016 16:31:20 +0200 From: "Michael S. Tsirkin" Message-ID: <20160224162344-mutt-send-email-mst@redhat.com> References: <1456239585-13324-1-git-send-email-den@openvz.org> <1456239585-13324-2-git-send-email-den@openvz.org> <20160223172048-mutt-send-email-mst@redhat.com> <56CC7ADD.5080508@openvz.org> <20160223174837-mutt-send-email-mst@redhat.com> <20160224100133.GA2519@rkaganb.sw.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160224100133.GA2519@rkaganb.sw.ru> Subject: Re: [Qemu-devel] [PATCH 1/2] virtio-balloon: export all balloon statistics List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Roman Kagan , "Denis V. Lunev" , Igor Redko , qemu-devel@nongnu.org On Wed, Feb 24, 2016 at 01:01:34PM +0300, Roman Kagan wrote: > On Tue, Feb 23, 2016 at 05:49:21PM +0200, Michael S. Tsirkin wrote: > > On Tue, Feb 23, 2016 at 06:29:33PM +0300, Denis V. Lunev wrote: > > > On 02/23/2016 06:24 PM, Michael S. Tsirkin wrote: > > > >On Tue, Feb 23, 2016 at 05:59:44PM +0300, Denis V. Lunev wrote: > > > >>From: Igor Redko > > > >> > > > >>We are making experiments with different autoballooning strategies > > > >>based on the guest behavior. Thus we need to experiment with different > > > >>guest statistics. For now every counter change requires QEMU recompilation > > > >>and dances with Libvirt. > > > >> > > > >>This patch introduces transport for unrecognized counters in virtio-balloon. > > > >>This transport can be used for measuring benefits from using new > > > >>balloon counters, before submitting any patches. Current alternative > > > >>is 'guest-exec' transport which isn't made for such delicate matters > > > >>and can influence test results. > > > >> > > > >>Originally all counters with tag >= VIRTIO_BALLOON_S_NR were ignored. > > > >>Instead of this we keep first (VIRTIO_BALLOON_S_NR + 32) counters from the > > > >>queue and pass unrecognized ones with the following names: 'x-stat-XXXX', > > > >>where XXXX is a tag number in hex. Defined counters are reported with their > > > >>regular names. > > > >> > > > >>Signed-off-by: Igor Redko > > > >>Signed-off-by: Denis V. Lunev > > > >>CC: Michael S. Tsirkin > > > >This seems to open the ABI to abuse. > > > >Seems like a reasonable way to experiment though. > > > >How about adding this within #if 0 statements? > > > >You can uncomment them for debugging ... > > > I'd prefer to have this enabled. > > > > > > Why do you think that it opens "abuse" way? > > > > Because people will use this to hack drivers and management tools > > bypassing qemu. > > I'm curious why you think it's a problem? Because we'll be stuck maintaining them with these x- names. > Even the existing stats are > simply propagated to the management level by qemu with no processing > other than assigning text labels. > > The proposed naming scheme for > unrecognized counters includes "x-" prefix which explicitly marks them > as unstable so people using them take their risk. > > One of the benefits is forward compatibility, so that counters that have > graduated into supported ones and have got their own number and name, > can be made to work with qemu that doesn't yet recognize them. Then management does start relying on the x- prefixed things, and once it's used to that it's a slippery slope. > [ Yes I've seen Den having posted a version hiding this under #ifdef, but I'd > still be interested to know why the initial proposal wasn't found > generally useful ] > > Thanks, > Roman.