netdev - Re: [PATCH RFC] virtio_net: enable tx interrupt

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Date:	Wed, 15 Oct 2014 12:33:48 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH RFC] virtio_net: enable tx interrupt

On 10/15/2014 07:11 AM, Michael S. Tsirkin wrote:
> On Wed, Oct 15, 2014 at 12:53:59AM +0300, Michael S. Tsirkin wrote:
>> >  static void skb_xmit_done(struct virtqueue *vq)
>> >  {
>> >  	struct virtnet_info *vi = vq->vdev->priv;
>> > +	struct send_queue *sq = &vi->sq[vq2txq(vq)];
>> >  
>> > -	/* Suppress further interrupts. */
>> > -	virtqueue_disable_cb(vq);
>> > -
> One note here: current code seems racy because of doing
> virtqueue_disable_cb from skb_xmit_done that I'm dropping here: there's
> no guarantee we don't get an interrupt while tx ring is running, and if
> that happens we can end up with interrupts disabled forever.
>

Looks harmless since:

- if event index is enabled, virtqueue_disable_cb() does nothing in fact.
- if event index is disabled, we don't depend on tx interrupt and when
num_free is low we will try to enable the tx interrupt again.
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