From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: Re: [PATCH net-next 8/8] vhost-net: reduce vq polling on tx zerocopy Date: Tue, 30 Oct 2012 11:47:45 -0400 Message-ID: <508FF6A1.5060201@redhat.com> References: <3e57e2cde71a4270a8fef395c31f5f0e8a130c28.1351524502.git.mst@redhat.com> Reply-To: vyasevic@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "David S. Miller" , Eric Dumazet , Andrew Morton , Alexander Duyck , Ian Campbell , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <3e57e2cde71a4270a8fef395c31f5f0e8a130c28.1351524502.git.mst@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 10/29/2012 11:49 AM, Michael S. Tsirkin wrote: > It seems that to avoid deadlocks it is enough to poll vq before > we are going to use the last buffer. This should be faster than > c70aa540c7a9f67add11ad3161096fb95233aa2e. > > Signed-off-by: Michael S. Tsirkin > --- > drivers/vhost/net.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 8e9de79..3967f82 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -197,8 +197,16 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, int status) > { > struct vhost_ubuf_ref *ubufs = ubuf->ctx; > struct vhost_virtqueue *vq = ubufs->vq; > - > - vhost_poll_queue(&vq->poll); > + int cnt = atomic_read(&ubufs->kref.refcount); > + > + /* > + * Trigger polling thread if guest stopped submitting new buffers: > + * in this case, the refcount after decrement will eventually reach 1 > + * so here it is 2. > + * We also trigger polling periodically after each 16 packets. > + */ > + if (cnt <= 2 || !(cnt % 16)) Why 16? Does it make sense to make it configurable? -vlad > + vhost_poll_queue(&vq->poll); > /* set len to mark this desc buffers done DMA */ > vq->heads[ubuf->desc].len = status ? > VHOST_DMA_FAILED_LEN : VHOST_DMA_DONE_LEN; >