Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759213Ab2EPReM (ORCPT ); Wed, 16 May 2012 13:34:12 -0400 Received: from e4.ny.us.ibm.com ([32.97.182.144]:43987 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753231Ab2EPReK (ORCPT ); Wed, 16 May 2012 13:34:10 -0400 Subject: Re: [V2 PATCH 9/9] vhost: zerocopy: poll vq in zerocopy callback From: Shirley Ma To: "Michael S. Tsirkin" Cc: Jason Wang , eric.dumazet@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, ebiederm@xmission.com, davem@davemloft.net In-Reply-To: <20120516151444.GC9934@redhat.com> References: <20120502033901.11782.13157.stgit@amd-6168-8-1.englab.nay.redhat.com> <20120502034254.11782.27314.stgit@amd-6168-8-1.englab.nay.redhat.com> <1337100630.8220.4.camel@oc3660625478.ibm.com> <4FB317C8.90002@redhat.com> <1337181027.10741.13.camel@oc3660625478.ibm.com> <20120516151444.GC9934@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 16 May 2012 10:32:05 -0700 Message-ID: <1337189525.10741.24.camel@oc3660625478.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 (2.28.3-24.el6) Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12051617-3534-0000-0000-00000870B3C6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2079 Lines: 55 On Wed, 2012-05-16 at 18:14 +0300, Michael S. Tsirkin wrote: > On Wed, May 16, 2012 at 08:10:27AM -0700, Shirley Ma wrote: > > On Wed, 2012-05-16 at 10:58 +0800, Jason Wang wrote: > > > >> drivers/vhost/vhost.c | 1 + > > > >> 1 files changed, 1 insertions(+), 0 deletions(-) > > > >> > > > >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > > >> index 947f00d..7b75fdf 100644 > > > >> --- a/drivers/vhost/vhost.c > > > >> +++ b/drivers/vhost/vhost.c > > > >> @@ -1604,6 +1604,7 @@ void vhost_zerocopy_callback(void *arg) > > > >> struct vhost_ubuf_ref *ubufs = ubuf->arg; > > > >> struct vhost_virtqueue *vq = ubufs->vq; > > > >> > > > >> + vhost_poll_queue(&vq->poll); > > > >> /* set len = 1 to mark this desc buffers done DMA */ > > > >> vq->heads[ubuf->desc].len = VHOST_DMA_DONE_LEN; > > > >> kref_put(&ubufs->kref, vhost_zerocopy_done_signal); > > > > Doing so, we might have redundant vhost_poll_queue(). Do you > know in > > > > which scenario there might be missing of adding and signaling > during > > > > zerocopy? > > > > > > Yes, as we only do signaling and adding during tx work, if there's > no > > > tx > > > work when the skb were sent, we may lose the opportunity to let > guest > > > know about the completion. It's easy to be reproduced with netperf > > > test. > > > > The reason which host signals guest is to free guest tx buffers, if > > there is no tx work, then it's not necessary to signal the guest > unless > > guest runs out of memory. The pending buffers will be released > > virtio_net device gone. > > > > What's the behavior of netperf test when you hit this situation? > > > > Thanks > > Shirley > > IIRC guest networking seems to be lost. It seems vhost_enable_notify is missing in somewhere else? Thanks Shirley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/