[fedora-arm] smsc95xx performance bug: eth vs usb

DJ Delorie dj at redhat.com
Sat May 28 00:53:57 UTC 2011

This is a weird bug, has anyone else seen or fixed it?

If you connect storage up to a pandaboard USB port (flash or sata),
you get about 5 MB/sec throughput.  Now, if you "ping -i 0.001" the
pandaboard from another host, you can increase the *storage*
performance to 22 MB/sec (for my disk, max 32 MB/sec on an x86
desktop).  Note that the ethernet device is itself also on the same
USB hub (on chip) as the device storage.

This tells me that something in the smsc95xx driver is either missing
an interrupt, or not polling fast enough, but I couldn't find

USB protocol analyzer shows that most of the time, the transfers are
happening at the full speed, so it's just stopping every once in a
while, killing performance.

Kernel is from the Fedora 15 development

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