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

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Message-ID: <20140509145745.GI7950@arm.com>
Date:	Fri, 9 May 2014 15:57:45 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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 03:50:02PM +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).

-- 
Catalin
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