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Message #00414
[Bug 709245] Re: panda: USB disk IO slow
I tested some more today (Oneiric 3.0 kernel) and the external USB drive
on a Panda.
With nosmp passed on the boot command line, the throughput is good with
or without the ping and about the same as using both cores and pinging
it.
Booting with both cores and putting cpu1 offline does not seem to affect
the behaviour - pinging leads to 4x or 5x throughput over not-pinging.
So it may be related to SMP scheduling. Also nosmp and putting one core
offline at runtime is apparently not the same ( I naively thought it
should be)
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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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