i.MX8MM Ethernet TX Bandwidth Fluctuations

Frieder Schrempf frieder.schrempf at kontron.de
Tue May 18 05:55:22 PDT 2021 


On 18.05.21 14:35, Joakim Zhang wrote:
> 
> Hi Dave,
> 
>> -----Original Message-----
>> From: Dave Taht <dave.taht at gmail.com>
>> Sent: 2021年5月17日 20:48
>> To: Joakim Zhang <qiangqing.zhang at nxp.com>
>> Cc: Frieder Schrempf <frieder.schrempf at kontron.de>; dl-linux-imx
>> <linux-imx at nxp.com>; netdev at vger.kernel.org;
>> linux-arm-kernel at lists.infradead.org
>> Subject: Re: i.MX8MM Ethernet TX Bandwidth Fluctuations
>>
>> On Mon, May 17, 2021 at 3:25 AM Joakim Zhang <qiangqing.zhang at nxp.com>
>> wrote:
>>>
>>>
>>> Hi Frieder,
>>>
>>>> -----Original Message-----
>>>> From: Frieder Schrempf <frieder.schrempf at kontron.de>
>>>> Sent: 2021年5月17日 15:17
>>>> To: Joakim Zhang <qiangqing.zhang at nxp.com>; dl-linux-imx
>>>> <linux-imx at nxp.com>; netdev at vger.kernel.org;
>>>> linux-arm-kernel at lists.infradead.org
>>>> Subject: Re: i.MX8MM Ethernet TX Bandwidth Fluctuations
>>>>
>>>> Hi Joakim,
>>>>
>>>> On 13.05.21 14:36, Joakim Zhang wrote:
>>>>>
>>>>> Hi Frieder,
>>>>>
>>>>> For NXP release kernel, I tested on i.MX8MQ/MM/MP, I can reproduce
>>>>> on
>>>> L5.10, and can't reproduce on L5.4.
>>>>> According to your description, you can reproduce this issue both
>>>>> L5.4 and
>>>> L5.10? So I need confirm with you.
>>>>
>>>> Thanks for looking into this. I could reproduce this on 5.4 and 5.10
>>>> but both kernels were official mainline kernels and **not** from the
>>>> linux-imx downstream tree.
>>> Ok.
>>>
>>>> Maybe there is some problem in the mainline tree and it got included
>>>> in the NXP release kernel starting from L5.10?
>>> No, this much looks like a known issue, it should always exist after adding
>> AVB support in mainline.
>>>
>>> ENET IP is not a _real_ multiple queues per my understanding, queue 0 is for
>> best effort. And the queue 1&2 is for AVB stream whose default bandwidth
>> fraction is 0.5 in driver. (i.e. 50Mbps for 100Mbps and 500Mbps for 1Gbps).
>> When transmitting packets, net core will select queues randomly, which
>> caused the tx bandwidth fluctuations. So you can change to use single queue if
>> you care more about tx bandwidth. Or you can refer to NXP internal
>> implementation.
>>> e.g.
>>> --- a/arch/arm64/boot/dts/freescale/imx8mq.dtsi
>>> +++ b/arch/arm64/boot/dts/freescale/imx8mq.dtsi
>>> @@ -916,8 +916,8 @@
>>>                                          <&clk
>> IMX8MQ_CLK_ENET_PHY_REF>;
>>>                                 clock-names = "ipg", "ahb", "ptp",
>>>                                               "enet_clk_ref",
>> "enet_out";
>>> -                               fsl,num-tx-queues = <3>;
>>> -                               fsl,num-rx-queues = <3>;
>>> +                               fsl,num-tx-queues = <1>;
>>> +                               fsl,num-rx-queues = <1>;
>>>                                 status = "disabled";
>>>                         };
>>>                 };
>>>
>>> I hope this can help you :)
>>
>> Patching out the queues is probably not the right thing.
>>
>> for starters... Is there BQL support in this driver? It would be helpful to have on
>> all queues.
> There is no BQL support in this driver, and BQL may improve throughput further, but should not be the root cause of this reported issue.
> 
>> Also if there was a way to present it as two interfaces, rather than one, that
>> would allow for a specific avb device to be presented.
>>
>> Or:
>>
>> Is there a standard means of signalling down the stack via the IP layer (a dscp?
>> a setsockopt?) that the AVB queue is requested?
>>
> AFAIK, AVB is scope of VLAN, so we can queue AVB packets into queue 1&2 based on VLAN-ID.

I had to look up what AVB even means, but from my current understanding it doesn't seem right that for non-AVB packets the driver picks any of the three queues in a random fashion while at the same time knowing that queue 1 and 2 have a 50% limitation on the bandwidth. Shouldn't there be some way to prefer queue 0 without needing the user to set it up or even arbitrarily limiting the number of queues as proposed above?

> 
> Best Regards,
> Joakim Zhang
>>> Best Regards,
>>> Joakim Zhang
>>>> Best regards
>>>> Frieder
>>>>
>>>>>
>>>>> Best Regards,
>>>>> Joakim Zhang
>>>>>
>>>>>> -----Original Message-----
>>>>>> From: Joakim Zhang <qiangqing.zhang at nxp.com>
>>>>>> Sent: 2021年5月12日 19:59
>>>>>> To: Frieder Schrempf <frieder.schrempf at kontron.de>; dl-linux-imx
>>>>>> <linux-imx at nxp.com>; netdev at vger.kernel.org;
>>>>>> linux-arm-kernel at lists.infradead.org
>>>>>> Subject: RE: i.MX8MM Ethernet TX Bandwidth Fluctuations
>>>>>>
>>>>>>
>>>>>> Hi Frieder,
>>>>>>
>>>>>> Sorry, I missed this mail before, I can reproduce this issue at
>>>>>> my side, I will try my best to look into this issue.
>>>>>>
>>>>>> Best Regards,
>>>>>> Joakim Zhang
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: Frieder Schrempf <frieder.schrempf at kontron.de>
>>>>>>> Sent: 2021年5月6日 22:46
>>>>>>> To: dl-linux-imx <linux-imx at nxp.com>; netdev at vger.kernel.org;
>>>>>>> linux-arm-kernel at lists.infradead.org
>>>>>>> Subject: i.MX8MM Ethernet TX Bandwidth Fluctuations
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> we observed some weird phenomenon with the Ethernet on our
>>>>>>> i.MX8M-Mini boards. It happens quite often that the measured
>>>>>>> bandwidth in TX direction drops from its expected/nominal value
>>>>>>> to something like 50% (for 100M) or ~67% (for 1G) connections.
>>>>>>>
>>>>>>> So far we reproduced this with two different hardware designs
>>>>>>> using two different PHYs (RGMII VSC8531 and RMII KSZ8081), two
>>>>>>> different kernel versions (v5.4 and v5.10) and link speeds of 100M and
>> 1G.
>>>>>>>
>>>>>>> To measure the throughput we simply run iperf3 on the target
>>>>>>> (with a short p2p connection to the host PC) like this:
>>>>>>>
>>>>>>>   iperf3 -c 192.168.1.10 --bidir
>>>>>>>
>>>>>>> But even something more simple like this can be used to get the
>>>>>>> info (with 'nc -l -p 1122 > /dev/null' running on the host):
>>>>>>>
>>>>>>>   dd if=/dev/zero bs=10M count=1 | nc 192.168.1.10 1122
>>>>>>>
>>>>>>> The results fluctuate between each test run and are sometimes 'good'
>>>> (e.g.
>>>>>>> ~90 MBit/s for 100M link) and sometimes 'bad' (e.g. ~45 MBit/s
>>>>>>> for 100M
>>>>>> link).
>>>>>>> There is nothing else running on the system in parallel. Some
>>>>>>> more info is also available in this post: [1].
>>>>>>>
>>>>>>> If there's anyone around who has an idea on what might be the
>>>>>>> reason for this, please let me know!
>>>>>>> Or maybe someone would be willing to do a quick test on his own
>>>> hardware.
>>>>>>> That would also be highly appreciated!
>>>>>>>
>>>>>>> Thanks and best regards
>>>>>>> Frieder
>>>>>>>
>>>>>>> [1]:
>>>>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%
>>>>>>> 2Fco
>>>>>>> mm
>>>>>>> u
>>>>>>>
>>>>>>
>>>>
>> nity.nxp.com%2Ft5%2Fi-MX-Processors%2Fi-MX8MM-Ethernet-TX-Bandwidth-
>>>>>>>
>>>>>>
>>>>
>> Fluctuations%2Fm-p%2F1242467%23M170563&data=04%7C01%7Cqiang
>>>>>>>
>>>>>>
>>>>
>> qing.zhang%40nxp.com%7C5d4866d4565e4cbc36a008d9109da0ff%7C686ea1d
>>>>>>>
>>>>>>
>>>>
>> 3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637559091463792932%7CUnkno
>>>>>>>
>>>>>>
>>>>
>> wn%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1ha
>>>>>>>
>>>>>>
>>>>
>> WwiLCJXVCI6Mn0%3D%7C1000&sdata=ygcThQOLIzp0lzhXacRLjSjnjm1FEj
>>>>>>> YSxakXwZtxde8%3D&reserved=0
>>
>>
>>
>> --
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>> 920%2F&data=04%7C01%7Cqiangqing.zhang%40nxp.com%7Cd11b7b331
>> db04c41799908d91932059b%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%
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>> p;sdata=IPW1MPLSnitX0HUttdLtZysknzokRN5fYVPXrbJQhaY%3D&reserve
>> d=0
>>
>> Dave Täht CTO, TekLibre, LLC

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