netdev - RE: [PATCH net-next 06/11] net: fec: transmit XDP frames in bulk

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Message-ID:
 <PAXPR04MB8510FED850459727118CAEA0888FA@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Wed, 14 Jan 2026 09:57:34 +0000
From: Wei Fang <wei.fang@....com>
To: Frank Li <frank.li@....com>
CC: Shenwei Wang <shenwei.wang@....com>, Clark Wang <xiaoning.wang@....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>,
	"ast@...nel.org" <ast@...nel.org>, "daniel@...earbox.net"
	<daniel@...earbox.net>, "hawk@...nel.org" <hawk@...nel.org>,
	"john.fastabend@...il.com" <john.fastabend@...il.com>, "sdf@...ichev.me"
	<sdf@...ichev.me>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>, "bpf@...r.kernel.org"
	<bpf@...r.kernel.org>
Subject: RE: [PATCH net-next 06/11] net: fec: transmit XDP frames in bulk

> On Tue, Jan 13, 2026 at 11:29:34AM +0800, Wei Fang wrote:
> > Currently, the driver writes the ENET_TDAR register for every XDP frame
> > to trigger transmit start. Frequent MMIO writes consume more CPU cycles
> > and may reduce XDP TX performance, so transmit XDP frames in bulk.
> >
> > Signed-off-by: Wei Fang <wei.fang@....com>
> > ---
> 
> Did you test light loading case? Any unexpected latency happen? sometime
> missing trigger is hard to find when heavy loading.
> 

I don't think a missing trigger event will occur. The driver doesn't wait until
the number of packets reaches a certain threshold before triggering the
transmission. The driver receives some packets in each batch, the number
is not fixed, but there is a threshold. After putting these packets on the TX
BD ring, transmission is triggered. Therefore, each batch will definitely trigger
transmission.