netdev - Re: [PATCH RFC v2 2/4] virtio_net: disable cb aggressively

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Date:   Tue, 13 Apr 2021 16:53:32 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>, Wei Wang <weiwan@...gle.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        Willem de Bruijn <willemb@...gle.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH RFC v2 2/4] virtio_net: disable cb aggressively


在 2021/4/13 下午1:47, Michael S. Tsirkin 写道:
> There are currently two cases where we poll TX vq not in response to a
> callback: start xmit and rx napi.  We currently do this with callbacks
> enabled which can cause extra interrupts from the card.  Used not to be
> a big issue as we run with interrupts disabled but that is no longer the
> case, and in some cases the rate of spurious interrupts is so high
> linux detects this and actually kills the interrupt.
>
> Fix up by disabling the callbacks before polling the tx vq.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>   drivers/net/virtio_net.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 82e520d2cb12..16d5abed582c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1429,6 +1429,7 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
>   		return;
>   
>   	if (__netif_tx_trylock(txq)) {
> +		virtqueue_disable_cb(sq->vq);
>   		free_old_xmit_skbs(sq, true);
>   		__netif_tx_unlock(txq);


Any reason that we don't need to enable the cb here?

And as we discussed in the past, it's probably the time to have a single 
NAPI for both tx and rx?

Thanks


>   	}
> @@ -1582,6 +1583,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
>   	bool use_napi = sq->napi.weight;
>   
>   	/* Free up any pending old buffers before queueing new ones. */
> +	virtqueue_disable_cb(sq->vq);
>   	free_old_xmit_skbs(sq, false);
>   
>   	if (use_napi && kick)