netdev - Re: [PATCH net-next v3 5/6] virtio_net: Add a lock for per queue RX coalesce

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Date: Fri, 12 Apr 2024 19:21:11 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Daniel Jurgens <danielj@...dia.com>
Cc: <netdev@...r.kernel.org>, <mst@...hat.com>, <jasowang@...hat.com>,
 <xuanzhuo@...ux.alibaba.com>, <virtualization@...ts.linux.dev>,
 <davem@...emloft.net>, <edumazet@...gle.com>, <pabeni@...hat.com>,
 <jiri@...dia.com>
Subject: Re: [PATCH net-next v3 5/6] virtio_net: Add a lock for per queue RX
 coalesce

On Fri, 12 Apr 2024 14:53:08 -0500 Daniel Jurgens wrote:
> Once the RTNL locking around the control buffer is removed there can be
> contention on the per queue RX interrupt coalescing data. Use a spin
> lock per queue.

Does not compile on Clang.

> +			scoped_guard(spinlock, &vi->rq[i].intr_coal_lock) {
> +				err = virtnet_send_rx_ctrl_coal_vq_cmd(vi, i,
> +								       vi->intr_coal_rx.max_usecs,
> +								       vi->intr_coal_rx.max_packets);
> +				if (err)
> +					return err;
> +			}

Do you really think this needs a scoped guard and 4th indentation level,
instead of just:

			..lock(..);
			err = virtnet_send_rx_ctrl_coal_vq_cmd(vi, i,
							       vi->intr_coal_rx.max_usecs,
							       vi->intr_coal_rx.max_packets);
			..unlock(..);
			if (err)
				return err;

> +		scoped_guard(spinlock, &vi->rq[i].intr_coal_lock) {
> +			vi->rq[i].intr_coal.max_usecs = ec->rx_coalesce_usecs;
> +			vi->rq[i].intr_coal.max_packets = ec->rx_max_coalesced_frames;
> +		}

:-|
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