netdev - Re: [PATCH net-next] net: xilinx: axienet: Configure and report coalesce parameters in DMAengine flow

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Message-ID: <6c99b7f5-b529-4efd-a065-1e0ebf01468e@lunn.ch>
Date: Thu, 29 May 2025 18:29:44 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: "Gupta, Suraj" <Suraj.Gupta2@....com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"vkoul@...nel.org" <vkoul@...nel.org>,
	"Simek, Michal" <michal.simek@....com>,
	"Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>,
	"horms@...nel.org" <horms@...nel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"git (AMD-Xilinx)" <git@....com>,
	"Katakam, Harini" <harini.katakam@....com>
Subject: Re: [PATCH net-next] net: xilinx: axienet: Configure and report
 coalesce parameters in DMAengine flow

> Yeah, but the reason is that you are trading latency for throughput.
> There is only one queue, so when the interface is saturated you will not
> get good latency anyway (since latency-sensitive packets will get
> head-of-line blocked). But when activity is sparse you can good latency
> if there is no coalescing. So I think coalescing should only be used
> when there is a lot of traffic. Hence why I only adjusted the settings
> once I implemented DIM. I think you should be able to implement it by
> calling net_dim from axienet_dma_rx_cb, but it will not be as efficient
> without NAPI.
> 
> Actually, if you are looking into improving performance, I think lack of
> NAPI is probably the biggest limitation with the dmaengine backend.

It latency is the goal, especially for mixing high and low priority
traffic, having BQL implemented is also important. Does this driver
have that?

	Andrew