I am building a USB interface to a radar data acquisition chassis based on the 
Cypress CY7C68013A.

While doing some speed testing I find that FreeBSD does ~4Mb/sec, but Linux 
does 17Mb/sec & OS X does 8-10Mb/sec.

It is using libusb-1.0 with the async API in a threaded app. I spawn a thread 
which sites in the following loop:

    while (!child_exit) {
        tout.tv_sec = 0;
        tout.tv_usec = 100000;
        libusb_handle_events_timeout(ctx, &tout);

The parent thread is the rest of the program which and handles reading data out 
of the completed transfers and forwarding them to the data processing children 
and re-submitting them to the USB stack.

I keep 8 transactions of 512 bytes each in flight. The device itself holds up 
to 4 packets in a FIFO until the PC is ready. Increasing the number of 
transactions in flight has no effect on performance.

Does anyone have a suggestion as to how I can look at improving performance? 
Deploying Linux is not really an option :)

The Linux PC is..
Linux fpgawork 2.6.32-28-generic #55-Ubuntu SMP Mon Jan 10 23:42:43 UTC 2011 
x86_64 GNU/Linux
The CPU is a Core 2 E6400 @ 2.13GHz on a Gigabyte 965P-DS3 rev 1 
(http://www.gigabyte.com/products/product-page.aspx?pid=2314#ov) which has an 
ICH8 chipset.

The FreeBSD PC is..
FreeBSD aumond8.gsoft.com.au 8.1-RELEASE FreeBSD 8.1-RELEASE #0: Mon Jul 19 
02:55:53 UTC 2010     r...@almeida.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC 
The CPU is a Core 2 E7500 @ 2.93GHz on a Supermicro C2SBA+ 
(http://www.supermicro.com/products/motherboard/Core/G33/C2SBA_.cfm) which has 
an ICH9 chipset.

Any patches welcome!


Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C

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