Re: Break 2.4 VM in five easy steps

Bernd Jendrissek
2001-06-08T07:38:54Z

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On Thu, Jun 07, 2001 at 03:38:35PM -0600, Brian D Heaton wrote:
> Maybe i'm missing something. I just tried this (with the 262144k/1
> and 128k/2048 params) and my results are within .1s of each other. This is
> without any special patches. Am I doing something wrong????

Oh, I don't mean the time elapsed, It's that nothing _else_ can happen
while dd is hogging the kernel.

> Oh yes -
>
> SMP - dual PIII866/133

Yes, this is what you are doing wrong ;)

My hypothesis is that in your case, one cpu gets pegged copying pages
from /dev/zero into dd's buffer, while the other cpu can do things like
updating mouse cursors, run setiathome, etc.

What happens if you do *two* dd-tortures with huge buffers at the same
time? And then, please don't happen to have a quad box!

I don't know if my symptom (loss of interactivity on heavy writing) is
related to swapoff -a causing the same symptom on deeply-swapped boxes.

BTW keep in mind my 4-liner is based more on voodoo than on analysis.

Bernd Jendrissek
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