From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:42199) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TdNvV-00044x-4N for qemu-devel@nongnu.org; Tue, 27 Nov 2012 11:22:30 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TdNvQ-0004ou-Vp for qemu-devel@nongnu.org; Tue, 27 Nov 2012 11:22:25 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48370) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TdNvQ-0004op-OC for qemu-devel@nongnu.org; Tue, 27 Nov 2012 11:22:20 -0500 Date: Tue, 27 Nov 2012 18:25:04 +0200 From: "Michael S. Tsirkin" Message-ID: <20121127162504.GA6210@redhat.com> References: <20121022111824.GA6916@amit.redhat.com> <1350913800.90009.YahooMailClassic@web163904.mail.gq1.yahoo.com> <20121023125503.GG19977@stefanha-thinkpad.redhat.com> <20121101091918.GA19405@amit.redhat.com> <20121101120410.GC3993@redhat.com> <20121101160721.GA9176@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121101160721.GA9176@redhat.com> Subject: Re: [Qemu-devel] [PATCH] virtio: limit avail bytes lookahead List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Amit Shah Cc: Stefan Hajnoczi , Bug 1066055 <1066055@bugs.launchpad.net>, qemu-devel@nongnu.org, Anthony Liguori , Edivaldo de Araujo Pereira On Thu, Nov 01, 2012 at 06:07:21PM +0200, Michael S. Tsirkin wrote: > Commit 0d8d7690850eb0cf2b2b60933cf47669a6b6f18f introduced > a regression in virtio-net performance because it looks > into the ring aggressively while we really only care > about a single packet worth of buffers. > To fix, add parameters limiting lookahead, and > use in virtqueue_avail_bytes. > > Signed-off-by: Michael S. Tsirkin > Reported-by: Edivaldo de Araujo Pereira Ping. Anthony - going to apply this? > --- > > Edivaldo could you please confirm this fixes regression? > > diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c > index d20bd8b..a761cdc 100644 > --- a/hw/virtio-serial-bus.c > +++ b/hw/virtio-serial-bus.c > @@ -297,7 +297,7 @@ size_t virtio_serial_guest_ready(VirtIOSerialPort *port) > if (use_multiport(port->vser) && !port->guest_connected) { > return 0; > } > - virtqueue_get_avail_bytes(vq, &bytes, NULL); > + virtqueue_get_avail_bytes(vq, &bytes, NULL, UINT_MAX, 0); > return bytes; > } > > diff --git a/hw/virtio.c b/hw/virtio.c > index ec8b7d8..f40a8c5 100644 > --- a/hw/virtio.c > +++ b/hw/virtio.c > @@ -336,7 +336,8 @@ static unsigned virtqueue_next_desc(hwaddr desc_pa, > } > > void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, > - unsigned int *out_bytes) > + unsigned int *out_bytes, > + unsigned max_in_bytes, unsigned max_out_bytes) > { > unsigned int idx; > unsigned int total_bufs, in_total, out_total; > @@ -385,6 +386,9 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, > } else { > out_total += vring_desc_len(desc_pa, i); > } > + if (in_total >= max_in_bytes && out_total >= max_out_bytes) { > + goto done; > + } > } while ((i = virtqueue_next_desc(desc_pa, i, max)) != max); > > if (!indirect) > @@ -392,6 +396,7 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, > else > total_bufs++; > } > +done: > if (in_bytes) { > *in_bytes = in_total; > } > @@ -405,12 +410,8 @@ int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes, > { > unsigned int in_total, out_total; > > - virtqueue_get_avail_bytes(vq, &in_total, &out_total); > - if ((in_bytes && in_bytes < in_total) > - || (out_bytes && out_bytes < out_total)) { > - return 1; > - } > - return 0; > + virtqueue_get_avail_bytes(vq, &in_total, &out_total, in_bytes, out_bytes); > + return in_bytes <= in_total && out_bytes <= out_total; > } > > void virtqueue_map_sg(struct iovec *sg, hwaddr *addr, > diff --git a/hw/virtio.h b/hw/virtio.h > index ac482be..1278328 100644 > --- a/hw/virtio.h > +++ b/hw/virtio.h > @@ -150,7 +150,8 @@ int virtqueue_pop(VirtQueue *vq, VirtQueueElement *elem); > int virtqueue_avail_bytes(VirtQueue *vq, unsigned int in_bytes, > unsigned int out_bytes); > void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes, > - unsigned int *out_bytes); > + unsigned int *out_bytes, > + unsigned max_in_bytes, unsigned max_out_bytes); > > void virtio_notify(VirtIODevice *vdev, VirtQueue *vq); >