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[warmcat <709245@xxxxxxxxxxxxxxxxxx>]

I meddled around with this last week via the Fedora ARM list, it was
simple to reproduce that pinging the Panda Ethernet from another machine
on the local network with -i0.001 yielded an effective 50% increase in
USB storage throughput at the Panda compared to it being left idle.

Neither RUNTIME_PM (suggested by Felipe Balbi at TI) nor USB_SUSPEND
were to blame since the issue stayed the same with those deconfigured.

It seems the issue may be to do with the Panda's hub / ethernet chip
idle / wakeup characteristics but since there are no hub registers in
there settable from Panda side AFAIK (there are some settable in the
missing EEPROM that can configure the hub / Ethernet bridge) I am out of
ideas to follow it up.

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https://bugs.launchpad.net/bugs/709245

Title:
  panda: USB disk IO slow

Status in Linaro Linux:
  Confirmed

Bug description:
  My Panda's USB seems to be significantly slower than a Beagle C4.

  hdparm shows buffered reads as ~12MB/s on the Panda, and about ~20-25MB/s on a Beagle C4 from the same
  external Lacie USB disk.

  Kernel is 2.6.37-1002-linaro-omap

  Disk shows as:

  [    5.170440] scsi 0:0:0:0: Direct-Access     LaCie    d2 quadra             PQ: 0 ANSI: 4
  [    5.172546] sd 0:0:0:0: Attached scsi generic sg0 type 0
  [    5.175415] sd 0:0:0:0: [sda] 976773168 512-byte logical blocks: (500 GB/465 GiB)

  The board is otherwise idle during the test.

  Doing perf_2.6.37-12 record -a dd if=/dev/sda of=/dev/null bs=4096
  count=100000

  shows :
      81.41%         swapper  [kernel.kallsyms]     [k] default_idle
       6.33%              dd  [kernel.kallsyms]     [k] __copy_to_user
       0.94%         swapper  [kernel.kallsyms]     [k] cpu_idle
       0.51%              dd  [kernel.kallsyms]     [k] __make_request
       0.51%  perf_2.6.37-12  [kernel.kallsyms]     [k] __copy_from_user

  
  which suggests it's not CPU constrained.

  Dave