Re: [patch] real-time enhanced page allocator and throttling

[Robert Love <rml@tech9.net>]

On Wed, 2003-08-06 at 01:41, Andrew Morton wrote:

> It's pretty easy to demonstrate the benefit of the balance_dirty_pages()
> change.  Just do:
> 
> while true
> do
> 	dd if=/dev/zero of=foo bs=1M count=512 conv=notrunc
> done
> 
> and also:
> 
> rm 1 ; sleep 3; time dd if=/dev/zero of=1 bs=16M count=1
> 
> The 16M dd normally takes 1.5 seconds (I'm pretty please with that btw. 
> Very repeatable and fair).  If you run the 16M dd with SCHED_FIFO it takes
> a repeatable 0.12 seconds.

This is what I did. Same results, basically.

What I did not do was prove that the xmms stalls went away for those who
were seeing that.

> So running a program off disk isn't a very good test.

No, its not. And in general, real-time tasks should not do disk I/O (at
least not via their core RT thread). And they should mlock() their
memory.

But circumstances do differ, and these changes are in the right
direction, I think. It also means e.g. someone can make xmms or whatever
real-time, and hopefully avoid the memory-related stalls that spawned
the discussion and this patch.

	Robert Love


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