linux-kernel - Re: 2.6.21-rc3-mm1 RSDL results

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Message-ID: <20070309211058.GH10394@waste.org>
Date:	Fri, 9 Mar 2007 15:10:58 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org
Subject: Re: 2.6.21-rc3-mm1 RSDL results

On Fri, Mar 09, 2007 at 02:46:24PM -0600, Matt Mackall wrote:
> A priori, this load should be manageable by RSDL as the interactive
> loads are all pretty small. So I wrote a little Python script that
> basically continuously memcpys some 16MB chunks of memory:
> 
> #!/usr/bin/python
> a = "a" * 16 * 1024 * 1024
> while 1:
>     b = a[1:] + "b"
>     a = b[1:] + "c"
> 
> I've got 1.5G of RAM, so I can run quite a few of these without
> killing my pagecache. This should test whether a) Beryl's actually
> running up against memory bandwidth issues and b) whether "simple"
> static loads work. As you can see, running 5 instances of this script
> leaves me in good shape still. 10 is still in "ok" territory, with top
> showing each getting 9.7-10% of the CPU. 15 starts to feel sluggish.
> 20 the mouse jumps a bit and I got an MP3 skip. 30 is getting pretty
> bad, but still not as bad as the make -j 5 load.
> 
> My suspicion is the problem lies in giving too much quanta to
> newly-started processes.

I've also tried 10+ instances of each of the following:

forkload:
#!/bin/sh
./forkload&

execload:
#!/bin/sh
exec ./execload

And it's quite well-behaved in both cases.

Also, if I run:

for a in 1 2 3 4 5; do mkdir $a; cp .config $a; make O=$a & done

..I get mostly good behavior with some occassional snags. Things run
much better than make -j 5. Unfortunately, that doesn't make my kernel
get built faster.

-- 
Mathematics is the supreme nostalgia of our time.
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