Re: SMP kernels on single processor machines

2004-05-24 Thread Benjamin Herrenschmidt
On Fri, 2004-05-21 at 22:58, Marius Groeger wrote: > FWIW, CONFIG_PREEMPT _does_ reduce the avarage scheduling latency. > It's still sort of soft real-time, but the effect is measurable (I'm > talking 2.4 kernels here, BTW) However, on desktop systems you > probably don need to worry about this,

Re: SMP kernels on single processor machines

2004-05-21 Thread Benjamin Herrenschmidt
On Fri, 2004-05-21 at 22:58, Marius Groeger wrote: > FWIW, CONFIG_PREEMPT _does_ reduce the avarage scheduling latency. > It's still sort of soft real-time, but the effect is measurable (I'm > talking 2.4 kernels here, BTW) However, on desktop systems you > probably don need to worry about this, b

Re: SMP kernels on single processor machines

2004-05-21 Thread Marius Groeger
On Fri, 21 May 2004, Lee Braiden wrote: > Benjamin Herrenschmidt wrote: > > > Yah, well... CONFIG_PREEMPT gives you all the problems of SMP without > > any benefit so :) > > Well, I know people argue about that, but I think it was you who advised > me to avoid PREEMPT before, so I'll take you

Re: SMP kernels on single processor machines

2004-05-21 Thread Lee Braiden
Benjamin Herrenschmidt wrote: Yah, well... CONFIG_PREEMPT gives you all the problems of SMP without any benefit so :) Well, I know people argue about that, but I think it was you who advised me to avoid PREEMPT before, so I'll take your word for it. But... what you said above was exact

Re: SMP kernels on single processor machines

2004-05-20 Thread Benjamin Herrenschmidt
On Thu, 2004-05-20 at 21:48, Lee Braiden wrote: > But I quit doing that at some point, after someone (authoritative, but I > can't remember the details) pointed out that it added complexity, > debugging issues, etc. Given that I *already* have problems with PPC > kernels -- latency/lockups, (pree

Re: SMP kernels on single processor machines

2004-05-20 Thread Lee Braiden
Jens Schmalzing wrote: SMP kernels run fine on single processor machines. I have repeatedly been told, however, that this bears a considerable performance hit on some hardware. Can anybody confirm or deny this? Even small hints would be appreciated. A long time ago, I used to compile SMP i

SMP kernels on single processor machines

2004-05-20 Thread Jens Schmalzing
Hi, putting together another release of the Debian kernel image packages, I am wondering whether we could get rid of half the packages by simply not supplying single processor flavours - after all, SMP kernels run fine on single processor machines. I have repeatedly been told, however, that this