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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 7 Jan 2010 14:41:51 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Paul Hartman <paul.hartman+linux@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Multi-file USB mass-storage copy from PC to Nokia N900 slow when 
	using CFQ

On Tue, Jan 5, 2010 at 5:07 PM, Paul Hartman
<paul.hartman+linux@...il.com> wrote:
> Hi,
>
> 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!

Can you try setting:
/sys/block/**your_device** /queue/iosched/fifo_expire_sync
to a large number, e.g. 5000 ?
CFQ operates pretty much like deadline w.r.t. normal writes, but uses
a much shorter interval to switch between two streams of writes, to
reduce latency of data hitting disk, and this could cause low
performance on flash devices, where writes that do not cover whole
blocks are painfully slow.

Corrado
>
> Thanks
> Paul
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@...r.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>



-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@...il.com
PhD - Department of Computer Science - University of Pisa, Italy
--------------------------------------------------------------------------
The self-confidence of a warrior is not the self-confidence of the average
man. The average man seeks certainty in the eyes of the onlooker and calls
that self-confidence. The warrior seeks impeccability in his own eyes and
calls that humbleness.
                               Tales of Power - C. Castaneda
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/