linux-kernel - Re: [PATCH net-next V4 2/3] virtio_net: support per queue interrupt coalesce command

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Message-ID: <f5823996fffad2f3c1862917772c182df74c74e7.camel@redhat.com>
Date:   Thu, 27 Jul 2023 15:28:32 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Gavin Li <gavinl@...dia.com>, mst@...hat.com, jasowang@...hat.com,
        xuanzhuo@...ux.alibaba.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        jiri@...dia.com, dtatulea@...dia.com
Cc:     gavi@...dia.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, Heng Qi <hengqi@...ux.alibaba.com>
Subject: Re: [PATCH net-next V4 2/3] virtio_net: support per queue interrupt
 coalesce command

On Tue, 2023-07-25 at 16:07 +0300, Gavin Li wrote:
> Add interrupt_coalesce config in send_queue and receive_queue to cache user
> config.
> 
> Send per virtqueue interrupt moderation config to underlying device in
> order to have more efficient interrupt moderation and cpu utilization of
> guest VM.
> 
> Additionally, address all the VQs when updating the global configuration,
> as now the individual VQs configuration can diverge from the global
> configuration.
> 
> Signed-off-by: Gavin Li <gavinl@...dia.com>
> Reviewed-by: Dragos Tatulea <dtatulea@...dia.com>
> Reviewed-by: Jiri Pirko <jiri@...dia.com>
> Acked-by: Michael S. Tsirkin <mst@...hat.com>

FTR, this patch is significantly different from the version previously
acked/reviewed, I'm unsure if all the reviewers are ok with the new
one.

[...]

>  static int virtnet_set_coalesce(struct net_device *dev,
>  				struct ethtool_coalesce *ec,
>  				struct kernel_ethtool_coalesce *kernel_coal,
>  				struct netlink_ext_ack *extack)
>  {
>  	struct virtnet_info *vi = netdev_priv(dev);
> -	int ret, i, napi_weight;
> +	int ret, queue_number, napi_weight;
>  	bool update_napi = false;
>  
>  	/* Can't change NAPI weight if the link is up */
>  	napi_weight = ec->tx_max_coalesced_frames ? NAPI_POLL_WEIGHT : 0;
> -	if (napi_weight ^ vi->sq[0].napi.weight) {
> -		if (dev->flags & IFF_UP)
> -			return -EBUSY;
> -		else
> -			update_napi = true;
> +	for (queue_number = 0; queue_number < vi->max_queue_pairs; queue_number++) {
> +		ret = virtnet_should_update_vq_weight(dev->flags, napi_weight,
> +						      vi->sq[queue_number].napi.weight,
> +						      &update_napi);
> +		if (ret)
> +			return ret;
> +
> +		if (update_napi) {
> +			/* All queues that belong to [queue_number, queue_count] will be
> +			 * updated for the sake of simplicity, which might not be necessary

It looks like the comment above still refers to the old code. Should
be:
	[queue_number, vi->max_queue_pairs]
			
Otherwise LGTM, thanks!

Paolo