netdev - Re: [PATCH v2 net-next resent] net: fec: Enable SOC specific rx-usecs coalescence default setting

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Message-ID:
 <PAXPR04MB9185CBA946F34FA6CD853DD489B02@PAXPR04MB9185.eurprd04.prod.outlook.com>
Date: Tue, 30 Jul 2024 13:47:18 +0000
From: Shenwei Wang <shenwei.wang@....com>
To: Joe Damato <jdamato@...tly.com>
CC: Wei Fang <wei.fang@....com>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Clark Wang <xiaoning.wang@....com>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH v2 net-next resent] net: fec: Enable SOC specific rx-usecs
 coalescence default setting



> -----Original Message-----
> From: Joe Damato <jdamato@...tly.com>
> Sent: Tuesday, July 30, 2024 5:17 AM
> To: Shenwei Wang <shenwei.wang@....com>
> Cc: Wei Fang <wei.fang@....com>; David S. Miller <davem@...emloft.net>;
> Eric Dumazet <edumazet@...gle.com>; Jakub Kicinski <kuba@...nel.org>;
> Paolo Abeni <pabeni@...hat.com>; Clark Wang <xiaoning.wang@....com>;
> imx@...ts.linux.dev; netdev@...r.kernel.org; dl-linux-imx <linux-
> imx@....com>
> Subject: [EXT] Re: [PATCH v2 net-next resent] net: fec: Enable SOC specific rx-
> usecs coalescence default setting
> 
> Caution: This is an external email. Please take care when clicking links or
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> 
> On Mon, Jul 29, 2024 at 02:35:27PM -0500, Shenwei Wang wrote:
> > Performance testing using iperf revealed no noticeable impact on
> > network throughput or CPU utilization.
> 
> I'm not sure this short paragraph addresses Andrew's comment:
> 
>   Have you benchmarked CPU usage with this patch, for a range of traffic
>   bandwidths and burst patterns. How does it differ?
> 
> Maybe you could provide more details of the iperf tests you ran? It seems odd
> that CPU usage is unchanged.
> 
> If the system is more reactive (due to lower coalesce settings and IRQs firing
> more often), you'd expect CPU usage to increase, wouldn't you?
> 

The driver operates under NAPI polling, where several factors influence IRQ triggering: 
NAPI polling weight, RX timer threshold, and RX frame count threshold. 
During iperf testing, my understanding is that the NAPI polling weight is likely the primary 
factor affecting triggering frequency, as IRQs are disabled during NAPI polling cycles.

Thanks,
Shenwei
	
> - Joe