Re: SCHED_ULE on desktop system

Am Montag, 17. September 2007 05:26:28 schrieb Jeff Roberson:
[snip]
> >> I run gkrellm and can tell at a glance when swap usage starts to
> >> increase. The linkage is clear and not terribly surprising. It may be
> >> that you need to add a bit more RAM.
> >
> > Yes, not surprising in the least.  When your system touches swap,
> > performance will drop to a tiny fraction of its normal performance.
> > Depending on your disk this could be 1% or lower.  Anyone who is seeing
> > poor interactive performance needs to rule this out as the cause.
>
> Ah, I think I know why people are reporting worse problems with ULE.  ULE
> is not properly accounting swtime so different threads are being chosen
> for swapout with ULE and 4BSD.  My test systems all have more than enough
> memory to do parallel buildworlds without swapping.  This is likely why I
> haven't run into this.
>
> I really need to fix p_swtime with ULE.  Could the people reporting bad
> behavior please verify whether or not you're seeing swapping activity?
> Even just looking for swap used in top will help me verify that this is
> the problem.

In my case swap wasn't used.
Of course do I have to expect overall performance loss if I don't have enough 
RAM, but even a heavily swapping machine shouldn't stop the mouse.
I can remember old FreeBSD 3.1 times when it was very common for all of my 
machines to use at least the size of RAM additionally for SWAP (about 16MB) 
and the machine was feeling smooth nevertheless.

I haven't tested if PREEMPTION makes any difference yet. I just remember I was 
really suprised that the difference between UP and SMP kernels on that 
machine is so extremely big.

Thanks for all your work!

-Harry