netdev - Re: Synopsys Ethernet QoS

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Date:   Tue, 13 Dec 2016 11:49:59 +0000
From:   Joao Pinto <Joao.Pinto@...opsys.com>
To:     Niklas Cassel <niklas.cassel@...s.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "Andy Shevchenko" <andy.shevchenko@...il.com>
CC:     David Miller <davem@...emloft.net>,
        Giuseppe CAVALLARO <peppe.cavallaro@...com>, <larper@...s.com>,
        <rabinv@...s.com>, netdev <netdev@...r.kernel.org>,
        <CARLOS.PALMINHA@...opsys.com>, <Jie.Deng1@...opsys.com>,
        Stephen Warren <swarren@...dia.com>, <pavel@....cz>
Subject: Re: Synopsys Ethernet QoS


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?

> 
> 
> 
> 
> 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
>