From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752698Ab2JaKb4 (ORCPT ); Wed, 31 Oct 2012 06:31:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21289 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756903Ab2JaK3D (ORCPT ); Wed, 31 Oct 2012 06:29:03 -0400 Date: Wed, 31 Oct 2012 12:31:20 +0200 From: "Michael S. Tsirkin" Cc: Vlad Yasevich , "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 Subject: [PATCHv2 net-next 8/8] vhost-net: reduce vq polling on tx zerocopy Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Mutt-Fcc: =sent To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It seems that to avoid deadlocks it is enough to poll vq before we are going to use the last buffer. This is faster than c70aa540c7a9f67add11ad3161096fb95233aa2e. Signed-off-by: Michael S. Tsirkin --- drivers/vhost/net.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 8e9de79..88beedb 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -197,8 +197,18 @@ 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 + * (the value 16 here is more or less arbitrary, it's tuned to trigger + * less than 10% of times). + */ + if (cnt <= 2 || !(cnt % 16)) + 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; -- MST