linux-kernel - Re: [RFC][PATCH 6/8] sched,idle: Avoid spurious wakeup IPIs

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Date:	Fri, 9 May 2014 19:02:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	James Hogan <james.hogan@...tec.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"luto@...capital.net" <luto@...capital.net>,
	"nicolas.pitre@...aro.org" <nicolas.pitre@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"umgwanakikbuti@...il.com" <umgwanakikbuti@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Will Deacon <Will.Deacon@....com>,
	ARM Kernel List <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC][PATCH 6/8] sched,idle: Avoid spurious wakeup IPIs

On Fri, May 09, 2014 at 03:57:45PM +0100, Catalin Marinas wrote:
> On Fri, May 09, 2014 at 03:50:02PM +0100, Peter Zijlstra wrote:
> > On Fri, May 09, 2014 at 03:40:34PM +0100, Catalin Marinas wrote:
> > 
> > > I wonder why we still need TIF_POLLING_NRFLAG for arm64. It was on arm
> > > until commit 16a8016372c42c7628eb (sanitize tsk_is_polling()). On arm64
> > > we use wfi for idle or a firmware call but in both cases the assumption
> > > is that we need an interrupt for waking up.
> > > 
> > > So I think we should remove this macro for arm64.
> > 
> > Does ARM64 support idle=poll? If so, you could keep it for that,
> > otherwise it does indeed appear to be pointless.
> 
> We don't support idle=poll either.
> 
> > As to 32bit ARM, are there SMP chips which do not have WFI?
> 
> No. WFI is even used for the secondary booting protocol (we need to send
> an IPI to get them going).

OK, so I'll queue a patch removing TIF_POLLING_NRFLAG for arm64.

Thanks!

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