linux-kernel - Re: [PATCH RFC] virtio_net: enable tx interrupt

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Message-ID: <20141014231154.GA23806@redhat.com>
Date:	Wed, 15 Oct 2014 02:11:54 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH RFC] virtio_net: enable tx interrupt

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.

> -	/* We were probably waiting for more output buffers. */
> -	netif_wake_subqueue(vi->dev, vq2txq(vq));
> +	if (napi_schedule_prep(&sq->napi)) {
> +		__napi_schedule(&sq->napi);
> +	}
>  }
>  
>  static unsigned int mergeable_ctx_to_buf_truesize(unsigned long mrg_ctx)
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