Messages in this thread | | | Date | Wed, 31 Dec 2014 00:13:31 +0100 | From | Beniamino Galvani <> | Subject | Re: [PATCH net-next] net: stmmac: add BQL support |
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On Mon, Dec 29, 2014 at 09:42:01AM -0800, Dave Taht wrote: > On Sun, Dec 28, 2014 at 1:48 PM, Beniamino Galvani <b.galvani@gmail.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@gmail.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.
I will try it, thanks.
> > 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/
I don't know if I have implemented it correctly, but I found that the improvement with xmit_more is so small to be barely observable, maybe because the cost for starting the hardware transmission is very low (it's a single mmio write).
Beniamino
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