SMP Strangeness

Simon Fowler simon at
Fri Jun 28 21:36:23 EST 2002

On Fri, Jun 28, 2002 at 02:56:25PM +1000, Saul Thurrowgood wrote:
> I would have thought the filesystem has no effect on speed reported by
> hdparm. Doesn't it just read from the raw device (/dev/sda)?
The reported speed from hdparm is completely seperate from the speed
from the filesystem - my two comments were seperate.

> Anyway, does seem very slow. I get 40 MB/s on each IDE disk, they are
> software striped to give about 72 MB/s.
*drool* I'd /love/ that kind of speed ;-)

In any case, the question was SMP scaling, and there the filesystem
/does/ have an effect. ext3 in particular spends a lot of it's time
under the BKL, which means it scales very badly. 

Still, I wouldn't have expected /that/ much of a slowdown - running
more processes than is efficient should degrade reasonably smoothly.


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