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[Ming Lei <709245@xxxxxxxxxxxxxxxxxx>]

Another interesting thing, enabling usbmon will increase performance a lot. 


root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 3.4598 s, 1.2 MB/s
root@tom-panda:~# cat /sys/kernel/debug/usb/usbmon/1u > /tmp/usbmon-1u&
[1] 1485
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 0.795455 s, 5.3 MB/s
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 0.278628 s, 15.1 MB/s
root@tom-panda:~# killall -9 cat
[1]+  Killed                  cat /sys/kernel/debug/usb/usbmon/1u > /tmp/usbmon-1u
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 5.0556 s, 830 kB/s
root@tom-panda:~# dd if=/dev/sda iflag=direct of=/dev/null bs=128K count=32
32+0 records in
32+0 records out
4194304 bytes (4.2 MB) copied, 3.2009 s, 1.3 MB/s

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

Title:
  panda: USB disk IO slow

Status in Linaro Ubuntu Evaluation Builds:
  Confirmed
Status in Linaro Linux:
  Confirmed
Status in “linux-ti-omap4” package in Ubuntu:
  Confirmed
Status in “linux-ti-omap4” source package in Oneiric:
  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

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