netdev - Re: high latency with imx8mm compared to imx6q

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Message-ID: <Y/K6xxqSIejCOuQk@lunn.ch>
Date:   Mon, 20 Feb 2023 01:11:51 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Richard Weinberger <richard@....at>
Cc:     wei fang <wei.fang@....com>,
        David Laight <David.Laight@...lab.com>,
        netdev <netdev@...r.kernel.org>,
        shenwei wang <shenwei.wang@....com>,
        xiaoning wang <xiaoning.wang@....com>,
        linux-imx <linux-imx@....com>
Subject: Re: high latency with imx8mm compared to imx6q

On Sat, Feb 18, 2023 at 02:20:53PM +0100, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
> > Von: "wei fang" <wei.fang@....com>
> > If you use the ethtool cmd, the minimum can only be set to 1.
> > But you can set the coalescing registers directly on your console,
> > ENET_RXICn[ICEN] (addr: base + F0h offset + (4d × n) where n=0,1,2) and
> > ENET_TXICn[ICEN] (addr: base + 100h offset + (4d × n), where n=0d to 2d)
> > set the ICEN bit (bit 31) to 0:
> > 0 disable Interrupt coalescing.
> > 1 disable Interrupt coalescing.
> > or modify you fec driver, but remember, the interrupt coalescing feature
> > can only be disable by setting the ICEN bit to 0, do not set the tx/rx
> > usecs/frames
> > to 0.
> 
> Disabling interrupt coalescing seems to make things much better. :-)

Another thing to consider. The FEC in imx8 gained support for EEE. So
if your link is otherwise idle, it could be put into low power mode,
and takes a little time to wake up. Like most MAC drivers, EEE is
broken on the FEC, but it could still be active. You might want to put
a printk() in fec_enet_eee_mode_set() and see if it is active. I would
not trust ethtool.

    Andrew