linux-kernel - Re: [PATCH net-next] net: stmmac: add BQL support

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Date:	Mon, 29 Dec 2014 09:42:01 -0800
From:	Dave Taht <dave.taht@...il.com>
To:	Beniamino Galvani <b.galvani@...il.com>
Cc:	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: stmmac: add BQL support

On Sun, Dec 28, 2014 at 1:48 PM, Beniamino Galvani <b.galvani@...il.com> wrote:
> On Sun, Dec 28, 2014 at 08:25:40AM -0800, Dave Taht wrote:
>> On Sun, Dec 28, 2014 at 6:57 AM, Beniamino Galvani <b.galvani@...il.com> wrote:
>> > Add support for Byte Queue Limits to the STMicro MAC driver.
>>
>> Thank you!
>>
>> > Tested on a Amlogic S805 Cortex-A5 board, where the use of BQL
>> > slightly decreases the ping latency from ~10ms to ~3ms when the
>> > 100Mbps link is saturated by TCP streams. No difference is
>> > observed at 1Gbps.
>>
>> I see the plural. With TSQ in place it is hard (without something like
>> the rrul test driving multiple streams) to drive a driver to
>> saturation with small numbers of flows. This was with pfifo_fast, not
>> sch_fq, at 100mbit?
>
> Hi Dave,
>
> yes, this was with pfifo_fast and I used 4 iperf TCP streams. The total
> throughput didn't seem to increase adding more streams.

>>
>> Can this board actually drive a full gigabit in the first place? Until
>> now most of the low end arm boards I have seen only came with
>> a 100mbit mac, and the gig ones lacking offloads seemed to peak
>> out at about 600mbit.
>
> I measured a throughput of 650mbit in rx and 600mbit in tx.

You might want to try the rrul test which tests both directions and
latency at the same time.

In my case I have been trying to find a low-cost chip that could do soft
rate limiting (htb) + fq_codel at up to 300mbit/sec, as that is about
the peak speed
we will be getting from cable modems, and these are horribly overbuffered,
at these speeds too, with 1.2sec of bidirectional latency observed at
120mbit/12mbit.

I'm open to crazy ideas like trying to find a use for the gpu, etc, to
get there.

>
>>
>> Under my christmas tree landed a quad core A5 (odroid-c1), also an
>> xgene and zedboard - both of the latter are a-needing BQL,
>> and I haven't booted the udroid yet. Hopefully it is the
>> same driver you just improved.
>
> I'm using the odroid-c1 too, with this tree based on the recent
> Amlogic mainline work:
>
>   https://github.com/bengal/linux/tree/meson8b

Oh, cool, thx!

> Unfortunately at the moment the support for the board is very basic
> (for example, SMP is not working yet) but it's enough to do some NIC
> tests.

Good to know. Have you looked at xmit_more yet?

http://lwn.net/Articles/615238/


> Beniamino



-- 
Dave Täht

http://www.bufferbloat.net/projects/bloat/wiki/Upcoming_Talks
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