linux-kernel - Re: [RFC PATCH net-next v2 6/7] net: ravb: Enable SW IRQ Coalescing for GbEth

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Date: Sat, 10 Feb 2024 21:42:28 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Paul Barker <paul.barker.ct@...renesas.com>, "David S . Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
CC: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, Wolfram Sang
	<wsa+renesas@...g-engineering.com>, <netdev@...r.kernel.org>,
	<linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH net-next v2 6/7] net: ravb: Enable SW IRQ Coalescing
 for GbEth

On 2/6/24 12:19 PM, Paul Barker wrote:

> Software IRQ Coalescing is required to improve network stack performance
> in the RZ/G2L SoC family and the RZ/G3S SoC, i.e. the SoCs which use the
> GbEth IP.
> 
> For the RZ/G2L, network throughput is comparable before and after this
> change. CPU usage during TCP RX testing dropped by 6.5% and during UDP
> RX testing dropped by 10%.
> 
> For the RZ/G2UL, network throughput is greatly increased by this change
> (results obtained with iperf3):
>   * TCP TX: 2.9% more throughput
>   * TCP RX: 1.1% more throughput
>   * UDP TX: similar throughput
>   * UDP RX: 41500% more throughput

   Wow! 8-)

> For the RZ/G3S we see improvements in network throughput similar to the
> RZ/G2UL.
> 
> The improvement of UDP RX bandwidth for the single core SoCs (RZ/G2UL &
> RZ/G3S) is particularly critical.
> 
> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
[...]

> diff --git a/drivers/net/ethernet/renesas/ravb.h b/drivers/net/ethernet/renesas/ravb.h
> index 55a7a08aabef..ca7a66759e35 100644
> --- a/drivers/net/ethernet/renesas/ravb.h
> +++ b/drivers/net/ethernet/renesas/ravb.h
> @@ -1078,6 +1078,7 @@ struct ravb_hw_info {
>  	unsigned nc_queues:1;		/* AVB-DMAC has RX and TX NC queues */
>  	unsigned magic_pkt:1;		/* E-MAC supports magic packet detection */
>  	unsigned half_duplex:1;		/* E-MAC supports half duplex mode */
> +	unsigned needs_irq_coalesce:1;	/* Requires SW IRQ Coalescing to achieve best performance */

   Is this really a hardware feature?
   Also, s/Requires SW/Needs software/ and s/to achieve best performance//,
please...

[...]

MBR, Sergey