netdev - Re: [PATCH 2/2] virtio_net: remove send completion interrupts and avoid TX queue overrun through packet drop

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Date:	Tue, 22 Mar 2011 19:26:44 -0700
From:	Shirley Ma <mashirle@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Herbert Xu <herbert@...dor.hengli.com.au>, rusty@...tcorp.com.au,
	davem@...emloft.net, kvm@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] virtio_net: remove send completion interrupts and
 avoid TX queue overrun through packet drop

On Tue, 2011-03-22 at 13:36 +0200, Michael S. Tsirkin wrote:
> diff --git a/drivers/virtio/virtio_ring.c
> b/drivers/virtio/virtio_ring.c
> index cc2f73e..6106017 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -185,11 +185,6 @@ int virtqueue_add_buf_gfp(struct virtqueue *_vq,
>         if (vq->num_free < out + in) {
>                 pr_debug("Can't add buf len %i - avail = %i\n",
>                          out + in, vq->num_free);
> -               /* FIXME: for historical reasons, we force a notify
> here if
> -                * there are outgoing parts to the buffer.  Presumably
> the
> -                * host should service the ring ASAP. */
> -               if (out)
> -                       vq->notify(&vq->vq);
>                 END_USE(vq);
>                 return -ENOSPC;
>         }
> 

With simply removing the notify here, it does help the case when TX
overrun hits too often, for example for 1K message size, the single
TCP_STREAM performance improved from 2.xGb/s to 4.xGb/s.

Thanks
Shirley

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