From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755633Ab3H3Elj (ORCPT ); Fri, 30 Aug 2013 00:41:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:7610 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755812Ab3H3ElZ (ORCPT ); Fri, 30 Aug 2013 00:41:25 -0400 From: Jason Wang To: mst@redhat.com, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Jason Wang Subject: [PATCH V2 6/6] vhost_net: correctly limit the max pending buffers Date: Fri, 30 Aug 2013 12:29:22 +0800 Message-Id: <1377836962-49780-7-git-send-email-jasowang@redhat.com> In-Reply-To: <1377836962-49780-1-git-send-email-jasowang@redhat.com> References: <1377836962-49780-1-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As Michael point out, We used to limit the max pending DMAs to get better cache utilization. But it was not done correctly since it was one done when there's no new buffers submitted from guest. Guest can easily exceeds the limitation by keeping sending packets. So this patch moves the check into main loop. Tests shows about 5%-10% improvement on per cpu throughput for guest tx. But a 5% drop on per cpu transaction rate for a single session TCP_RR. Signed-off-by: Jason Wang --- drivers/vhost/net.c | 15 ++++----------- 1 files changed, 4 insertions(+), 11 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index d09c17c..592e1f2 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -363,6 +363,10 @@ static void handle_tx(struct vhost_net *net) if (zcopy) vhost_zerocopy_signal_used(net, vq); + if ((nvq->upend_idx + vq->num - VHOST_MAX_PEND) % UIO_MAXIOV == + nvq->done_idx) + break; + head = vhost_get_vq_desc(&net->dev, vq, vq->iov, ARRAY_SIZE(vq->iov), &out, &in, @@ -372,17 +376,6 @@ static void handle_tx(struct vhost_net *net) break; /* Nothing new? Wait for eventfd to tell us they refilled. */ if (head == vq->num) { - int num_pends; - - /* If more outstanding DMAs, queue the work. - * Handle upend_idx wrap around - */ - num_pends = likely(nvq->upend_idx >= nvq->done_idx) ? - (nvq->upend_idx - nvq->done_idx) : - (nvq->upend_idx + UIO_MAXIOV - - nvq->done_idx); - if (unlikely(num_pends > VHOST_MAX_PEND)) - break; if (unlikely(vhost_enable_notify(&net->dev, vq))) { vhost_disable_notify(&net->dev, vq); continue; -- 1.7.1