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[Michael Sparmann <theseven@xxxxxxx>]

When running just dd at 1MB block size, I get ~5.5MB/s.

When running with sudo ping -q -i.0100 localhost in the background, ping causes 1% CPU load, and I get ~10MB/s at 1MB block size and these ping statistics:
6228 packets transmitted, 6227 received, 0% packet loss, time 97329ms
rtt min/avg/max/mdev = 0.000/0.053/2.899/0.050 ms

When running with sudo ping -q -i.0099 localhost in the background, ping causes 100% (one core) CPU load, and I get ~20MB/s at 1MB block size and these ping statistics:
10339 packets transmitted, 10337 received, 0% packet loss, time 93032ms
rtt min/avg/max/mdev = 0.000/0.033/0.946/0.031 ms

Now why does ping process about twice as many packets but use 100 times
more CPU (and get better response times) when I reduce the delay by just
one percent? There's something fishy going on here...

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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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