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SubjectRe: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM

* Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:

> On Thu, May 26, 2011 at 02:26:23PM +0200, Ingo Molnar wrote:
> >
> > * Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > > Sort this by reverting to the old behaviour for this situation
> > > and perform a full remote wake-up.
> >
> > Btw., ARM should consider switching most of its subarchitectures
> > to !__ARCH_WANT_INTERRUPTS_ON_CTXSW - enabling irqs during
> > context switches is silly and now expensive as well.
>
> Not going to happen. The reason we do it is because most of the
> CPUs have to (slowly) flush their caches during switch_mm(), and to
> have IRQs off over the cache flush means that we lose IRQs.

How much time does that take on contemporary ARM hardware, typically
(and worst-case)?

Thanks,

Ingo


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