netdev - Re: [PATCH net-next RFC 4/4] virtio-net: clean tx descriptors from rx napi

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Date:   Mon, 6 Mar 2017 13:04:47 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next RFC 4/4] virtio-net: clean tx descriptors from rx napi

On Mon, Mar 6, 2017 at 12:43 PM, Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>>> +static void virtnet_poll_cleantx(struct receive_queue *rq)
>>> +{
>>> +       struct virtnet_info *vi = rq->vq->vdev->priv;
>>> +       unsigned int index = vq2rxq(rq->vq);
>>> +       struct send_queue *sq = &vi->sq[index];
>>> +       struct netdev_queue *txq = netdev_get_tx_queue(vi->dev, index);
>>> +
>>> +       __netif_tx_lock(txq, smp_processor_id());
>>> +       free_old_xmit_skbs(sq, sq->napi.weight);
>>> +       __netif_tx_unlock(txq);
>>
>>
>> Should we check tx napi weight here? Or this was treated as an independent
>> optimization?
>
> Good point. This was not intended to run in no-napi mode as is.
> With interrupts disabled most of the time in that mode, I don't
> expect it to be worthwhile using in that case. I'll add the check
> for sq->napi.weight != 0.

I'm wrong here. Rx interrupts are not disabled, of course. It is
probably worth benchmarking, then.