Re: I/O Scheduling results in poor responsiveness

>     Why is the command below all that is needed to bring the system to
> it's knees? Why doesn't the io scheduler, CFQ, which is supposed to be
> all about fairness starve other processes? Example, if I open a new file
> in vim, and hold down "i" while this is running it will pause the
> display of new "i"s for seconds, sometimes until the dd write is
> completely finished. Another example is applications like firefox,
> thunderbird, xchat, and pidgin will stop refreshing for 10+ seconds.
>
>  dd if=/dev/zero of=test-file bs=2M count=2048
>
>  I understand the main difference between using oflag=direct or not
> relates to if the io scheduler is used, and if the file is cached or
> not. I can see this clearly by watching cached rise without
> oflag=direct, stay the same with it, and go way down when I delete the
> file after running dd without oflag=direct.
>
>  The system in question is running Fedora 8. It is an E6600, 4gb memory,
> and 2x300gb Seagate sata drives. The drives are setup with md raid 1,
> and the filesystem is ext3. But I also see this with plenty of other
> systems with more cpu, less cpu, less memory, raid, and no raid.