netdev - Re: Synopsys Ethernet QoS

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Date:   Tue, 13 Dec 2016 12:50:11 +0000
From:   Lars Persson <lars.persson@...s.com>
To:     Niklas Cassel <niklass@...s.com>
CC:     Joao Pinto <Joao.Pinto@...opsys.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "David Miller" <davem@...emloft.net>,
        Giuseppe CAVALLARO <peppe.cavallaro@...com>,
        Rabin Vincent <rabinv@...s.com>,
        netdev <netdev@...r.kernel.org>,
        "CARLOS.PALMINHA@...opsys.com" <CARLOS.PALMINHA@...opsys.com>,
        "Jie.Deng1@...opsys.com" <Jie.Deng1@...opsys.com>,
        Stephen Warren <swarren@...dia.com>,
        "pavel@....cz" <pavel@....cz>
Subject: Re: Synopsys Ethernet QoS


> 13 dec. 2016 kl. 13:31 skrev Niklas Cassel <Niklas.Cassel@...s.com>:
> 
> 
> 
>> On 12/13/2016 12:49 PM, Joao Pinto wrote:
>> Hi Niklas,
>> 
>> Às 4:25 PM de 12/12/2016, Niklas Cassel escreveu:
>>> 
>>>> On 12/12/2016 11:19 AM, Joao Pinto wrote:
>>>> Hi,
>>>> 
>>>> Às 1:44 AM de 12/10/2016, Florian Fainelli escreveu:
>>>>>> Le 12/09/16 à 16:16, Andy Shevchenko a écrit :
>>>>>> On Sat, Dec 10, 2016 at 12:52 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
>> (snip...)
>> 
>> 
>>>> @Rabin Vincent: Hi Rabin. Since Axis is more familiar with the synopsys/*qos*
>>>> driver would it be possible for you to make an initial analysis of what has to
>>>> be merged into Stmmac? This way the development would speed-up.
>>> I can answer that question.
>>> 
>>> I've sent out 12 patches to the stmmac driver
>>> (all patches are included in the current net-next tree),
>>> with these patches the stmmac driver works properly on Axis hardware
>>> (we use Synopsys GMAC 4.10a synthesized with multiple TX queues).
>>> stmmac's DT binding has also been extended with properties that
>>> existed in DWC EQoS's DT binding, such as no-pbl-x8, txpbl, rxpbl.
>>> 
>>> Since we have no problem updating the DTB together with the kernel,
>>> we will simply move to using the start using the stmmac driver,
>>> with stmmac's DT binding.
>>> 
>>> However, I've noticed that NVIDIA has extended the DWC EQoS DT binding,
>>> I don't how easy it would be for them to switch to stmmac's DT binding.
>>> (Adding Stephen Warren to CC.)
>>> 
>>> The reset sequence that Lars Persson was worried about is not an issue
>>> with the stmmac driver.
>> Great! So you saying that stmmac works great with AXIS hardware and no need to
>> merge specific code from AXIS' *qos* driver?
> 
> Yes. From Axis point of view, we are done.
> stmmac works and we will move to that driver + DT binding.
> 
> However, it seems like Stephen Warren will NAK if you try to remove
> synopsys/dwc_eth_qos.c before
> Documentation/devicetree/bindings/net/stmmac.txt
> is compatible with
> Documentation/devicetree/bindings/net/snps,dwc-qos-ethernet.txt
> 
> You might want to sync with him. I have no idea, but perhaps they are
> only using a subset of all the available properties. Perhaps,
> only implementing what they are using might be enough, I don't know.
> I couldn't find their DTS in arch/arm/dts.
> I guess you might want to know David Miller's opinion,
> since he's the one who decides in the end.

I will also NACK removal of dwc_eth_qos.c until the binding is implemented elsewhere.


> 
>>> 
>>> 
>>> 
>>> There are some performance problems with the stmmac driver though:
>>> 
>>> When running iperf3 with 3 streams:
>>> iperf3 -c 192.168.0.90 -P 3 -t 30
>>> iperf3 -c 192.168.0.90 -P 3 -t 30 -R
>>> 
>>> I get really bad fairness between the streams.
>>> 
>>> This appears to be an issue with how TX IRQ coalescing is implemented in stmmac.
>>> Disabling TX IRQ coalescing in the stmmac driver makes the problem go away.
>>> We have a local patch that implements TX IRQ coalescing in the dwceqos driver,
>>> and we don't see the same problem.
>>> 
>>> Also netperf TCP_RR and UDP_RR gives really bad results compared to the
>>> dwceqos driver (without IRQ coalescing).
>>> 2000 transactions/sec vs 9000 transactions/sec.
>>> Turning TX IRQ coalescing off and RX interrupt watchdog off in stmmac
>>> gives the same performance. I guess it's a trade off, low CPU usage
>>> vs low latency, so I don't know how important TCP_RR/UDP_RR really is.
>>> 
>>> The best thing would be to get a good working TX IRQ coalesce
>>> implementation with HR timers in stmmac.
>>> Perhaps it should also be investigated if the RX interrupt watchdog
>>> timeout should have a lower default value.
>>> 
>>> 
>>> 
>>>> Thanks to all.
>>>> 
>>>> Joao
>