From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:59873) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TTxGd-0003gH-0C for qemu-devel@nongnu.org; Thu, 01 Nov 2012 12:05:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TTxGT-0002vS-BL for qemu-devel@nongnu.org; Thu, 01 Nov 2012 12:05:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24543) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TTxGT-0002u8-2p for qemu-devel@nongnu.org; Thu, 01 Nov 2012 12:05:05 -0400 Date: Thu, 1 Nov 2012 18:07:21 +0200 From: "Michael S. Tsirkin" Message-ID: <20121101160721.GA9176@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121101120410.GC3993@redhat.com> Subject: [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 , Edivaldo de Araujo Pereira , qemu-devel@nongnu.org, Anthony Liguori , Bug 1066055 <1066055@bugs.launchpad.net> 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 --- 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);