[Bloat] USB Ethernet Adapters with BQL?

[Bloat] USB Ethernet Adapters with BQL?

[Noah Causin]

Hi,

I was looking into getting a USB 3.0 Gigabit Ethernet adapter, and I was 
trying to find ones that had BQL support in their drivers.

Are there any good ones out there, or is there something related to USB 
that reduces this feature's effectiveness?

Thank you,

Noah

Re: [Bloat] USB Ethernet Adapters with BQL?

[Jonathan Morton]

> On 17 Jun, 2016, at 22:42, Noah Causin <n0manletter@gmail.com> wrote:
> 
> I was looking into getting a USB 3.0 Gigabit Ethernet adapter, and I was trying to find ones that had BQL support in their drivers.
> 
> Are there any good ones out there, or is there something related to USB that reduces this feature's effectiveness?

Because the USB protocol gives greater decoupling between host and device than PCI (or PCIe) does, USB Ethernet adapters don’t have a general, explicit signal to indicate when packets are actually transmitted on the wire, or an easy low-latency way to discover the instantaneous buffer fill level (besides “full” vs. “not full”).  This makes implementing BQL challenging.

I’m not personally aware of any USB adapters with BQL.  That doesn’t mean there aren’t any.

 - Jonathan Morton

Re: [Bloat] USB Ethernet Adapters with BQL?

[Dave Taht]

most usb network adaptors tend to use the "usbnet" infrastructure,
which tries to minimize interrupts, but
also tends towards trying to only keep 5ms or so of data "in flight",
so leveraging fq_codel on top of a usb ethernet device at the qdisc
layer tends to show a small, but measurable benefit, at 100 mbit or a
gbit.

We tend to run out of speed of the bus on usb2 for gbit.

this is not quite true on slow things like the raspberry pi1, where we
run out of cpu first.

somewhere around here I have benchmarks of this sort of usb stuff on
various platforms, but in the end the results were reasonable enough
(latency/jitter less than 20ms typically) for me to not stress out
about it.

Please feel free to try a comparison between pfifo_fast and fq_codel
on top of a given usb-ethernet device.

...

the infrastructure for usb 3G modems is a whole other ball of wax. It
is a more or less mandated part
of the standards that at least 32k exist on the other side of the
device and the underlying code was pretty overbuffered too (and 3G can
get well below a mbit on uploads).... I have longed for something
bql-like there.

usb-wifi also tends towards utterly horrific.

...

I also am using usb "gadget ethernet" drivers with some success on the
getchip and beaglebone, with
mildly better results for fq_codel over pfifo_fast. The getchip does
not have fq_codel yet, however, and they had a bit of trouble getting
the combined cdc/serial ethernet gadget to work on their latest kernel
release.

(aside from being in a losing battle currently with systemd on device
renaming - usb gadget ethernet works great with openwrt).

[Bloat] WiFi over SDIO [was: USB Ethernet Adapters with BQL?]

[Juliusz Chroboczek]

> Because the USB protocol

Jonathan, Dave,

Can you tell us a few words about SDIO Wifi modules?  Do they have the
same issues?  What's the latency like?

-- Juliusz