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Message #00409
[Bug 709245] Re: panda: USB disk IO slow
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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