Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933088AbbBIIj5 (ORCPT ); Mon, 9 Feb 2015 03:39:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46090 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933042AbbBIIjt (ORCPT ); Mon, 9 Feb 2015 03:39:49 -0500 From: Jason Wang To: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, mst@redhat.com Cc: pagupta@redhat.com, Jason Wang Subject: [PATCH RFC v5 net-next 1/6] virtio_ring: fix virtqueue_enable_cb() when only 1 buffers were pending Date: Mon, 9 Feb 2015 03:39:20 -0500 Message-Id: <1423471165-34243-2-git-send-email-jasowang@redhat.com> In-Reply-To: <1423471165-34243-1-git-send-email-jasowang@redhat.com> References: <1423471165-34243-1-git-send-email-jasowang@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1760 Lines: 40 We currently does: bufs = (avail->idx - last_used_idx) * 3 / 4; This is ok now since we only try to enable the delayed callbacks when the queue is about to be full. This may not work well when there is only one pending buffer in the virtqueue (this may be the case after tx interrupt was enabled). Since virtqueue_enable_cb() will return false which may cause unnecessary triggering of napis. This patch correct this by only calculate the four thirds when bufs is not one. Signed-off-by: Jason Wang --- drivers/virtio/virtio_ring.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 00ec6b3..545fed5 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -636,7 +636,10 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) * entry. Always do both to keep code simple. */ vq->vring.avail->flags &= cpu_to_virtio16(_vq->vdev, ~VRING_AVAIL_F_NO_INTERRUPT); /* TODO: tune this threshold */ - bufs = (u16)(virtio16_to_cpu(_vq->vdev, vq->vring.avail->idx) - vq->last_used_idx) * 3 / 4; + bufs = (u16)(virtio16_to_cpu(_vq->vdev, vq->vring.avail->idx) - + vq->last_used_idx); + if (bufs != 1) + bufs = bufs * 3 / 4; vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs); virtio_mb(vq->weak_barriers); if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) - vq->last_used_idx) > bufs)) { -- 1.8.3.1 -- 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/