On 10/3/10 4:54 PM, Pyun YongHyeon wrote:
On Sat, Oct 02, 2010 at 08:41:57AM +0200, Hans Petter Selasky wrote:
On Saturday 02 October 2010 02:11:00 Pyun YongHyeon wrote:

I don't know how long it had been there but it seems current USB
stack does not honor fairness of TX/RX on USB ethernet controller.
Unidirectional performance test(UDP) or most-unidirectional
performance(TCP) test works well without problems. However if heavy
TX/RX traffic hits controller at the same time either TX or RX is
not served at all. I'm under the impression that whenever TX work
is done it seems USB reschedules next pending TX again instead of
processing RX such that RX is starved to death. This can be easily
reproduced on two hosts with the netperf performance test.
Whenever both hosts send tiny UDP datagrams to the other host
either TX or RX packet counters are not increasing until the end
of the UDP torture test. The number of EHCI interrupt is about 8K/s
while test is in progress so I think it reached its maximum
processing limit. After netperf testing, it can still process TX/RX
packets even though it dropped too many RX packets. But these
dropped packets are not counted so netstat(1) shows 0 dropped
frames even though it lost millions of packets.

Hans, do you have any idea what's going on here?
You can use the following netperf command on both hosts after
running netserver.
%netperf -c -H ip_addr_of_other_host -tUDP_STREAM -l 300 -- -m 1

Another odd thing I noticed is number of interrupts does not go
down to 0 after the testing. It constantly generates 1k/s
interrupts after that.
Maybe we are triggering a bug. Can you enable USB debugging to figure out what
data lengths are transmitted or received.

In the middle of testing? If yes, that would be meaningless as it
would generate bunch of messages. The test case generates payload
size 1 UDP datagrams with full speed so enabling debug messages
will change timing. Note, I'm exercising number of packets per
second, not number of bytes per second.

USB EHCI uses round robin, so this is either USB device problem or a test-
program software failure.

I'm pretty sure the benchmark program is not broken, so either
axe(4) or USB stack could be wrong here. I see three issues from
the UDP torture test.
  - Either TX or RX could be starved to death. If you start TX test
    first, RX would be stuck. If you start RX test first, TX would
    be stuck.
  - The number of packets sent or received are much lower than
    For TX case, the number of packets sent per second is exactly 8k
    which is much less than that of non-USB controllers. For gigabit

that is a big clue.
the USB hardware uses an 8 thousand time per second clock for it's internal polling.

    controllers number of TX packets could be several hundred
    thousands per second. For RX packets it shows 14K/s packets with
    8K/s interrupts. I thought USB ethernet controllers can send
    more than 8k packets per second. Because the number of
    interrupts per second and 8k packets per second is the same,
    this also make me wonder there could be some relations there.
  - Number of interrupts does not go back to 0 after the testing.

I'll let you know if I find some clue but it may take long time as
I'm not familiar with USB stack. :-(

Check the CPU usage of the host computer during the test. Do you see anything?

I didn't notice odd thing except 8k/s interrupts.

The only way I stop that interrupts was to
down the ue0 interface with "ifconfig ue0 down" command.
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