netdev - Re: [PATCH net] virtio_net: Avoid sending unnecessary vq coalescing commands

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Message-ID: <20240730182020.75639070@kernel.org>
Date: Tue, 30 Jul 2024 18:20:20 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Heng Qi <hengqi@...ux.alibaba.com>
Cc: netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>, Jason
 Wang <jasowang@...hat.com>, virtualization@...ts.linux.dev, Eugenio
 Pérez <eperezma@...hat.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH net] virtio_net: Avoid sending unnecessary vq coalescing
 commands

On Mon, 29 Jul 2024 20:47:55 +0800 Heng Qi wrote:
> Subject: [PATCH net] virtio_net: Avoid sending unnecessary vq coalescing commands

subject currently reads like this is an optimization, could you
rephrase?

> From the virtio spec:
> 
> 	The driver MUST have negotiated the VIRTIO_NET_F_VQ_NOTF_COAL
> 	feature when issuing commands VIRTIO_NET_CTRL_NOTF_COAL_VQ_SET
> 	and VIRTIO_NET_CTRL_NOTF_COAL_VQ_GET.
> 
> The driver must not send vq notification coalescing commands if
> VIRTIO_NET_F_VQ_NOTF_COAL is not negotiated. This limitation of course
> applies to vq resize.
> 
> Fixes: f61fe5f081cf ("virtio-net: fix the vq coalescing setting for vq resize")
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 29 +++++++++++++++++------------
>  1 file changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 0383a3e136d6..eb115e807882 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -3708,6 +3708,7 @@ static int virtnet_set_ringparam(struct net_device *dev,
>  	u32 rx_pending, tx_pending;
>  	struct receive_queue *rq;
>  	struct send_queue *sq;
> +	u32 pkts, usecs;
>  	int i, err;
>  
>  	if (ring->rx_mini_pending || ring->rx_jumbo_pending)
> @@ -3740,11 +3741,13 @@ static int virtnet_set_ringparam(struct net_device *dev,
>  			 * through the VIRTIO_NET_CTRL_NOTF_COAL_TX_SET command, or, if the driver
>  			 * did not set any TX coalescing parameters, to 0.
>  			 */
> -			err = virtnet_send_tx_ctrl_coal_vq_cmd(vi, i,
> -							       vi->intr_coal_tx.max_usecs,
> -							       vi->intr_coal_tx.max_packets);
> -			if (err)
> -				return err;
> +			if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_VQ_NOTF_COAL)) {
> +				usecs = vi->intr_coal_tx.max_usecs;
> +				pkts = vi->intr_coal_tx.max_packets;
> +				err = virtnet_send_tx_ctrl_coal_vq_cmd(vi, i, usecs, pkts);
> +				if (err)
> +					return err;

Can you check the feature inside the
virtnet_send_.x_ctrl_coal_vq_cmd() helpers?
5 levels of indentation is a bit much
-- 
pw-bot: cr