Re: [RFC][PATCH -rt] sched: fully ignore RT tasks for CFSload-balancing

From: Peter Zijlstra
Date: Wed Aug 26 2009 - 15:06:01 EST

On Wed, 2009-08-26 at 11:52 -0700, Darren Hart wrote:
> Peter Zijlstra wrote:
> > Since -rt runs IRQs and SoftIRQs as RT tasks and load-balancing is done
> > from softirq context, there is always at least one RT task (and very
> > likely multiple) running when we balance.
> >
> > The current (and totally broken) interaction between RT tasks and CFS
> > load-balancing makes it so that we'll try to evacuate a significant
> > amount of tasks due to RT tasks being runnable.
> >
> > Solve this in another broken way by not accounting RT tasks at all.
> >
> > This will likely break another class of cases, but until we can properly
> > fix this, we might as well do this.
> Peter,
> Do we know why this became a problem lately? I don't recall seeing load
> balancing issues like this way back around 2.6.21 or 22 when CFS was
> released. Is the cpu_load stuff fairly recent?

The earlier problem solved by the previous patch was caused by tglx
tinkering with the cpu_load computation.

This particular problem I'm not sure about, afaict it should have been
present a long long time.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at