linux-kernel - RE: [PATCH V3 net-next] net: fec: add XDP

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Message-ID: <AM5PR04MB3139D8AAAB6B96B58425BBA08809A@AM5PR04MB3139.eurprd04.prod.outlook.com>
Date:   Fri, 4 Aug 2023 03:06:11 +0000
From:   Wei Fang <wei.fang@....com>
To:     Jesper Dangaard Brouer <hawk@...nel.org>,
        Jesper Dangaard Brouer <jbrouer@...hat.com>,
        Jakub Kicinski <kuba@...nel.org>
CC:     "brouer@...hat.com" <brouer@...hat.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        Shenwei Wang <shenwei.wang@....com>,
        Clark Wang <xiaoning.wang@....com>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "john.fastabend@...il.com" <john.fastabend@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Andrew Lunn <andrew@...n.ch>
Subject: RE: [PATCH V3 net-next] net: fec: add XDP_TX feature support

> > The FEC of i.MX8MP-EVK has dma_coherent=false, and as I mentioned
> > above, I did not see an obvious difference in the performance. :(
> 
> That is surprising - given the results.
> 
> (see below, lack of perf/diff might be caused by Ethernet flow-control).
> 
> >
> >>> The result of the current modification.
> >>> root@...8mpevk:~# ./xdp2 eth0
> >>> proto 17:     260180 pkt/s
> >>
> >> These results are*significantly*  better than reported in patch-1.
> >> What happened?!?
> >>
> > The test environment is slightly different, in patch-1, the FEC port
> > was directly connected to the port of another board. But in the latest
> > test, the ports of the two boards were connected to a switch, so the
> > ports of the two boards are not directly connected.
> >
> 
> Hmm, I've seen this kind of perf behavior of direct-connected or via switch
> before. The mistake I made was, that I had not disabled Ethernet flow-control.
> The xdp2 XDP_TX program will swap the mac addresses, and send the packet
> back to the packet generator (running pktgen), which will get overloaded
> itself and starts sending Ethernet flow-control pause frames.
> 
> Command line to disable:
>   # ethtool -A eth0 rx off tx off
> 
> Can I ask/get you to make sure that Ethernet flow-control is disabled (on
> both generator and DUT (to be on safe-side)) and run the test again?
> 
The flow-control was not disabled before, so according to your suggestion,
I disable the flow-control on the both boards and run the test again, the
performance is slightly improved, but still can not see a clear difference
between the two methods. Below are the results.

Result: use "sync_dma_len" method
root@...8mpevk:~# ./xdp2 eth0
proto 17:     258886 pkt/s
proto 17:     258879 pkt/s
proto 17:     258872 pkt/s
proto 17:     258312 pkt/s
proto 17:     258926 pkt/s
proto 17:     259057 pkt/s
proto 17:     258437 pkt/s
proto 17:     259242 pkt/s
proto 17:     258665 pkt/s
proto 17:     258779 pkt/s
proto 17:     259209 pkt/s

Result: use the current method
root@...8mpevk:~# ./xdp2 eth0
proto 17:     258752 pkt/s
proto 17:     258672 pkt/s
proto 17:     258317 pkt/s
proto 17:     258787 pkt/s
proto 17:     258757 pkt/s
proto 17:     258542 pkt/s
proto 17:     258829 pkt/s
proto 17:     258480 pkt/s
proto 17:     258859 pkt/s
proto 17:     258918 pkt/s
proto 17:     258782 pkt/s
proto 17:     259086 pkt/s
proto 17:     258337 pkt/s