linux-kernel - Re: linux-next: build failure after merge of the tip tree

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Message-ID: <20140120101345.GC3694@twins.programming.kicks-ass.net>
Date:	Mon, 20 Jan 2014 11:13:45 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Len Brown <lenb@...nel.org>
Cc:	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	linux-next@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the tip tree

On Mon, Jan 20, 2014 at 09:30:21AM +0100, Peter Zijlstra wrote:
> Then make them so. The fact was that most of the mwait idle sites
> were bloody broken. And the single mwait_idle_with_hints() function
> presents a single nice function that does all the required magics.

To stress this a bit more; have a look see at mwwait_idle_with_hints();
it does a whole lot of subtle magic.

 - current_{set,clr}_polling*(), these are crucial in not missing and
   wrecking NEED_RESCHED state.

 - X86_FEATURE_CLFLUSH_MONTIOR quirk

 - Does the monitor(); if (!need_resched()) mwait() thing.

All of those are required for a correct and functional idle loop. And
I've seen sites where any or all of the above were missing/broken.

Not unifying the lot into a simple usable function is just stupid --
history has shown people simply cannot be trusted to get this right.
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