libusb performance on 8.1

[Daniel O'Connor]

[re-sent from the correct address]

Hi,
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);
   }
   ugsio_cancelusb();

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     root at almeida.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386
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!

Thanks.
--
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
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