Subject: Re: [PATCH net-next] net: ti: icssg_prueth: Add SW TX / RX Coalescing based on hrtimers

From: Simon Horman <[email-masked]>
Date: Sat, 27 Apr 2024 14:41:20 +0100

On Wed, Apr 24, 2024 at 02:48:23PM +0530, MD Danish Anwar wrote:
> Add SW IRQ coalescing based on hrtimers for RX and TX data path for ICSSG
> driver, which can be enabled by ethtool commands:
> 
> - RX coalescing
>   ethtool -C eth1 rx-usecs 50
> 
> - TX coalescing can be enabled per TX queue
> 
>   - by default enables coalesing for TX0
>   ethtool -C eth1 tx-usecs 50
>   - configure TX0
>   ethtool -Q eth0 queue_mask 1 --coalesce tx-usecs 100
>   - configure TX1
>   ethtool -Q eth0 queue_mask 2 --coalesce tx-usecs 100
>   - configure TX0 and TX1
>   ethtool -Q eth0 queue_mask 3 --coalesce tx-usecs 100 --coalesce
> tx-usecs 100
> 
> Minimum value for both rx-usecs and tx-usecs is 20us.
> 
> Comapared to gro_flush_timeout and napi_defer_hard_irqs this patch

nit: Compared

> allows to enable IRQ coalescing for RX path separately.
> 
> Signed-off-by: MD Danish Anwar <[email-masked]>

...

> @@ -190,19 +191,35 @@ int emac_tx_complete_packets(struct prueth_emac *emac, int chn,
>  	return num_tx;
>  }
>  
> +static enum hrtimer_restart emac_tx_timer_callback(struct hrtimer *timer)
> +{
> +	struct prueth_tx_chn *tx_chns =
> +			container_of(timer, struct prueth_tx_chn, tx_hrtimer);
> +
> +	enable_irq(tx_chns->irq);
> +	return HRTIMER_NORESTART;
> +}
> +
>  static int emac_napi_tx_poll(struct napi_struct *napi_tx, int budget)
>  {
>  	struct prueth_tx_chn *tx_chn = prueth_napi_to_tx_chn(napi_tx);
>  	struct prueth_emac *emac = tx_chn->emac;
> +	bool tdown = false;
>  	int num_tx_packets;
>  
> -	num_tx_packets = emac_tx_complete_packets(emac, tx_chn->id, budget);
> +	num_tx_packets = emac_tx_complete_packets(emac, tx_chn->id, budget, &tdown);

Please consider limiting lines to 80 columns wide in Networking code.

>  
>  	if (num_tx_packets >= budget)
>  		return budget;
>  
> -	if (napi_complete_done(napi_tx, num_tx_packets))
> -		enable_irq(tx_chn->irq);
> +	if (napi_complete_done(napi_tx, num_tx_packets)) {
> +		if (unlikely(tx_chn->tx_pace_timeout_ns && !tdown))
> +			hrtimer_start(&tx_chn->tx_hrtimer,
> +				      ns_to_ktime(tx_chn->tx_pace_timeout_ns),
> +				      HRTIMER_MODE_REL_PINNED);
> +		else
> +			enable_irq(tx_chn->irq);
> +	}
>  
>  	return num_tx_packets;
>  }

...

> @@ -870,7 +889,12 @@ int emac_napi_rx_poll(struct napi_struct *napi_rx, int budget)
>  	}
>  
>  	if (num_rx < budget && napi_complete_done(napi_rx, num_rx))
> -		enable_irq(emac->rx_chns.irq[rx_flow]);
> +		if (unlikely(emac->rx_pace_timeout_ns))
> +			hrtimer_start(&emac->rx_hrtimer,
> +				      ns_to_ktime(emac->rx_pace_timeout_ns),
> +				      HRTIMER_MODE_REL_PINNED);
> +		else
> +			enable_irq(emac->rx_chns.irq[rx_flow]);

clang-18 and gcc-13 both complain about the if/else logic above.
I think it would be best to add {} to the outer if statement.

>  	return num_rx;
>  }

...