linux-kernel - Re: idle issues running sembench on 128 cpus

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Date:	Thu, 5 May 2011 15:58:19 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <andi@...stfloor.org>
cc:	Dave Kleikamp <dkleikamp@...il.com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, lenb@...nel.org, paulmck@...ibm.com
Subject: Re: idle issues running sembench on 128 cpus

On Thu, 5 May 2011, Thomas Gleixner wrote:
> On Thu, 5 May 2011, Andi Kleen wrote:
> > > No, it does not even need refcounting. We can access it outside of the
> > 
> > Ok.
> > 
> > > lock as this is atomic context called on the cpu which is about to go
> > > idle and therefor the device cannot go away. Easy and straightforward
> > > fix.
> > 
> > Ok. Patch appended. Looks good?
> 
> Mostly. See below.
>  
> > BTW why must the lock be irqsave?
> 
> Good question. Probably safety frist paranoia :)
> 
> Indeed that code should only be called from irq disabled regions, so
> we could avoid the irqsave there. Otherwise that needs to be irqsave
> for obvious reasons.

Just looked through all the call sites. Both intel_idle and
processor_idle notify ENTER with interrups disabled, but EXIT with
interrupts enabled. So when we want to remove irqsave from the
spinlock that needs to be fixed as well.

Thanks,

        tglx
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