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[Launchpad Bug Tracker <709245@xxxxxxxxxxxxxxxxxx>]

You have been subscribed to a public bug by Dr. David Alan Gilbert (davidgil-uk):

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

** Affects: linux-linaro
     Importance: Medium
     Assignee: Mian Yousaf Kaukab (mian-yousaf-kaukab)
         Status: Confirmed

-- 
panda: USB disk IO slow
https://bugs.launchpad.net/bugs/709245
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