netdev - RE: high latency with imx8mm compared to imx6q

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Message-ID: <b4fc00958e0249208b5aceecfa527161@AcuMS.aculab.com>
Date:   Fri, 17 Feb 2023 20:49:23 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Richard Weinberger' <richard@....at>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "wei.fang@....com" <wei.fang@....com>,
        "shenwei.wang@....com" <shenwei.wang@....com>,
        "xiaoning.wang@....com" <xiaoning.wang@....com>,
        "linux-imx@....com" <linux-imx@....com>
Subject: RE: high latency with imx8mm compared to imx6q

From: Richard Weinberger
> Sent: 17 February 2023 16:53
...
> I'm investigating into latency issues on an imx8mm system after
> migrating from imx6q.
> A regression test showed massive latency increases when single/small packets
> are exchanged.
> 
> A simple test using ping exhibits the problem.
> Pinging the very same host from the imx8mm has a way higher RTT than from the imx6.
> 
> Ping, 100 packets each, from imx6q:
> rtt min/avg/max/mdev = 0.689/0.851/1.027/0.088 ms
> 
> Ping, 100 packets each, from imx8mm:
> rtt min/avg/max/mdev = 1.073/2.064/2.189/0.330 ms
> 
> You can see that the average RTT has more than doubled.
...

Is it just interrupt latency caused by interrupt coalescing
to avoid excessive interrupts?

	David

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