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

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Message-ID: <20110526125007.GA27083@elte.hu>
Date:	Thu, 26 May 2011 14:50:07 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Frank Rowand <frank.rowand@...sony.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()"
 locks up on ARM


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

> On Thu, May 26, 2011 at 02:26:23PM +0200, Ingo Molnar wrote:
> > 
> > * Peter Zijlstra <peterz@...radead.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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