Re: usb-storage nice value

[Jan Engelhardt <jengelh@linux01.gwdg.de>]

On May 18 2007 08:15, DervishD wrote:

>Date: Fri, 18 May 2007 08:15:12 +0200
>From: DervishD <lkml@dervishd.net>
>To: Stefan Richter <stefanr@s5r6.in-berlin.de>
>Cc: linux-kernel@vger.kernel.org
>Subject: Re: usb-storage nice value

Try ionice.

>> DervishD wrote:
>> >     I'm having problems when reading/writing to external USB harddisks:
>> > my *internal* harddisk stalls from time to time, so watching a movie
>> > while copying data is a PITA (well, if the movie is bad, the leaps help
>> > a bit...).
>> 
>> If the internal harddisk is source or target of these copy operations...
>
>    Not...
> 
>> ...
>> > is there any way of modifying the pdflush behaviour so
>> > large buffered writes are less "agressive" and doesn't block apps which
>> > are just reading?
>> 
>> ...then switching to another IO scheduler might perhaps help.
>> 
>> # cat /sys/block/hda/queue/scheduler
>> 
>> # echo deadline > /sys/block/hda/queue/scheduler
>

Or try echo 10 >/proc/sys/kernel/dirty_ratio

>    That's another thing I wanted to test, but I'm already using
>"deadline" scheduler. How about changing "read_ahead_kb" to a much
>higher value so there's plenty of data buffered? The problem seems to
>be, according to Alan Cox, that my VIA mobo fills completely the PCI bus
>when doing IO bursts, so I can take advantage of that "bug" and fill the
>bus when reading.
>
>    My only doubt is if it will affect performance negatively in other
>usage patterns (e.g. while writing CD's, since the hard disk will take
>the bus on each read operation, and will read more than the current 128
>kB).


	Jan
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