From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55278) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zr94y-00064m-87 for qemu-devel@nongnu.org; Tue, 27 Oct 2015 14:34:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zr94t-0003Dy-5x for qemu-devel@nongnu.org; Tue, 27 Oct 2015 14:34:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36020) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zr94t-0003Dl-0T for qemu-devel@nongnu.org; Tue, 27 Oct 2015 14:34:35 -0400 Date: Tue, 27 Oct 2015 20:34:32 +0200 From: "Michael S. Tsirkin" Message-ID: <20151027203140-mutt-send-email-mst@redhat.com> References: <1445935663-31971-1-git-send-email-mst@redhat.com> <1445935663-31971-2-git-send-email-mst@redhat.com> <20151027161954.GG5626@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151027161954.GG5626@stefanha-x1.localdomain> Subject: Re: [Qemu-devel] [PATCH 1/6] virtio: introduce virtio_map List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Igor Mammedov , qemu-devel@nongnu.org On Tue, Oct 27, 2015 at 04:19:54PM +0000, Stefan Hajnoczi wrote: > On Tue, Oct 27, 2015 at 10:47:56AM +0200, Michael S. Tsirkin wrote: > > This will still fail if there's no space left in the sg, but luckily max > > queue size in use is currently 256, while max sg size is 1024, so we > > should be OK even is all entries happen to cross a single DIMM boundary. > > Don't forget about indirect descriptors. They can use all 1024 iovecs, > regardless of virtqueue size, so virtqueue size of 256 isn't the true > maximum. Not according to the spec - virtio spec says vq size is the maximum size of a chain. > I'm worried that we could now see failures due to non-contiguous HVAs. Does linux guest create chains > vq size then? Does it actually have 1024 hardcoded somewhere? -- MST