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

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Message-ID: <f445b132-98c5-4f38-bd3e-172bc8645a03@linux.dev>
Date: Thu, 29 May 2025 12:35:09 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Andrew Lunn <andrew@...n.ch>
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

On 5/29/25 12:29, Andrew Lunn wrote:
>> 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

Yes, see commit c900e49d58eb ("net: xilinx: axienet: Implement BQL").

--Sean