linux-kernel - Re: Multi-file USB mass-storage copy from PC to Nokia N900 slow when using CFQ

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Date:	Tue, 5 Jan 2010 22:25:00 +0000
From:	Sitsofe Wheeler <sitsofe@...oo.com>
To:	Paul Hartman <paul.hartman+linux@...il.com>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Subject: Re: Multi-file USB mass-storage copy from PC to Nokia N900 slow
	when using CFQ

On Tue, Jan 05, 2010 at 10:07:22AM -0600, Paul Hartman wrote:
> Hi,

I'm going to CC Jens on this email as he's the block device maintainer
and might be in the better position to comment on this.

> Copying more than one file from my PC (kernel 2.6.32) to my Nokia N900
> over USB mass storage mode is very slow when CFQ is the i/o scheduler.
> The target uses vfat filesystem.
> 
> I am using iotop to monitor the I/O in general, plus I performed the
> following test. file1 and file2 are each 700M and both housed on a
> ramdrive for this test. They were deleted from the destination between
> runs.
> 
> # one file at a time with sync in-between, fast speeds:
> $ sync; time sh -c "cp file1 /mnt/usb; sync; cp file2 /mnt/usb; sync"
> 
> real    1m25.697s
> user    0m0.005s
> sys     0m2.509s
> 
> # copy two files in a row, then sync, speed is bad:
> $ sync; time sh -c "cp file1 file2 /mnt/usb; sync"
> 
> real    6m51.439s
> user    0m0.007s
> sys     0m2.615s
> 
> 
> Using all I/O schedulers, the speed of the first test was the same. So
> it's only related to writing more than 1 file to the N900. The timing
> results for the second test ended up as such:
> 
> cfq: 6m51.439s
> noop: 3m0.733s
> anticipatory: 1m44.348s
> deadline: 1m36.804s
> 
> 
> Also, in 2.6.31 the speed was four times slower, so the removal of old
> pdflush code may have made a difference in this case. Copying 1
> gigabyte takes about 1 minute at optimal speed, about 5 minutes using
> CFQ in kernel 2.6.32, and took about 20 minutes using CFQ in kernel
> 2.6.31.
> 
> I thought you may be interested in case there's room to improve the
> scheduler.  If you want any other info let me know!
> 
> Thanks
> Paul
> --
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-- 
Sitsofe | http://sucs.org/~sits/
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