From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42644) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zr7Eq-0002wn-0y for qemu-devel@nongnu.org; Tue, 27 Oct 2015 12:36:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zr7Ek-0002Ja-Aq for qemu-devel@nongnu.org; Tue, 27 Oct 2015 12:36:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:52450) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zr7Ek-0002JP-5v for qemu-devel@nongnu.org; Tue, 27 Oct 2015 12:36:38 -0400 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (Postfix) with ESMTPS id B9D68341AC9 for ; Tue, 27 Oct 2015 16:36:37 +0000 (UTC) Date: Tue, 27 Oct 2015 14:36:35 -0200 From: Eduardo Habkost Message-ID: <20151027163635.GH4180@thinpad.lan.raisama.net> References: <1445852815-85168-1-git-send-email-imammedo@redhat.com> <20151026120943-mutt-send-email-mst@redhat.com> <20151026142432.4a8ca282@nial.brq.redhat.com> <20151027084706-mutt-send-email-mst@redhat.com> <20151027094837.65185c94@nial.brq.redhat.com> <20151027105059-mutt-send-email-mst@redhat.com> <20151027101456.7c333167@nial.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151027101456.7c333167@nial.brq.redhat.com> Subject: Re: [Qemu-devel] [PATCH v2] pc: memhp: enforce minimal 128Mb alignment for pc-dimm List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, "Michael S. Tsirkin" On Tue, Oct 27, 2015 at 10:14:56AM +0100, Igor Mammedov wrote: > On Tue, 27 Oct 2015 10:53:08 +0200 > "Michael S. Tsirkin" wrote: > > > On Tue, Oct 27, 2015 at 09:48:37AM +0100, Igor Mammedov wrote: > > > On Tue, 27 Oct 2015 10:31:21 +0200 > > > "Michael S. Tsirkin" wrote: > > > > > > > On Mon, Oct 26, 2015 at 02:24:32PM +0100, Igor Mammedov wrote: > > > > > Yep it's workaround but it works around QEMU's broken virtio > > > > > implementation in a simple way without need for guest side changes. > > > > > > > > > > Without foreseeable virtio fix it makes memory hotplug unusable and even > > > > > more so if there were a virtio fix it won't fix old guests since you've > > > > > said that virtio fix would require changes of both QEMU and guest sides. > > > > > > > > What makes it not foreseeable? > > > > Apparently only the fact that we have a work-around in place so no one > > > > works on it. I can code it up pretty quickly, but I'm flat out of time > > > > for testing as I'm going on vacation soon, and hard freeze is pretty > > > > close. > > > I can lend a hand for testing part. > > > > > > > > > > > GPA space is kind of cheap, but wasting it in chunks of 512M > > > > seems way too aggressive. > > > hotplug region is sized with 1Gb alignment reserve per DIMM so we aren't > > > actually wasting anything here. > > > > > > > If I allocate two 1G DIMMs, what will be the gap size? 512M? 1G? > > It's too much either way. > minimum would be 512, and if backend is 1Gb-hugepage gap will be > backend's natural alignment (i.e. 1Gb). Is backend configuration even allowed to affect the machine ABI? We need to be able to change backend configuration when migrating the VM to another host. -- Eduardo