linux-kernel - Re: Sluggish system responsiveness on I/O

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Date:	Sun, 19 Nov 2006 19:34:55 +0100
From:	Mike Galbraith <efault@....de>
To:	Lee Revell <rlrevell@...-job.com>
Cc:	Christian <christiand59@....de>, linux-kernel@...r.kernel.org
Subject: Re: Sluggish system responsiveness on I/O

On Sun, 2006-11-19 at 12:44 -0500, Lee Revell wrote:
> On Sun, 2006-11-19 at 08:51 +0100, Mike Galbraith wrote:
> > That makes sense, I/O tasks don't generally hold the cpu for extended
> > periods, whereas a cpu bound task does.
> 
> So what can we do about I/O intensive tasks that also want a lot of CPU,
> for example, the bloatier Gnome/KDE apps?  Evolution is the worst for
> me.

Evolution has big trouble with the ext3 (and maybe others) journal.
I've _never_ seen evolution having scheduler priority problems, only
journal problems (absolutely every damn time hefty I/O is going on).

What should we do about I/O tasks that decide to use massive cpu?

IMHO, absolutely nothing beyond what ever we decide to do with any other
cpu intensvive task.  There is nothing special about scheduling I/O
heavy tasks.  If it uses massive cpu for sustained periods, it must pay
the price.  In the meantime, an I/O intensive task that decides to use
heavy cpu will round-robin at relatively high frequency with every other
"interactive" task, which may also be doing a burst of cpu heavy work.
The reason for doing that cpu intensive burst just doesn't matter.

Currently, we special case I/O tasks to limit the dynamic priority boost
they can get via I/O.  I think that is wrong.

	-Mike

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