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Date: Thu, 19 Dec 2013 18:50:37 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Len Brown <lenb@kernel.org>,
        x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Len Brown <len.brown@intel.com>, stable@vger.kernel.org,
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        Thomas Gleixner <tglx@linutronix.de>, Mike Galbraith <efault@gmx.de>,
        Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH] x86 idle: repair large-server 50-watt idle-power
 regression
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On Thu, Dec 19, 2013 at 06:25:35PM +0100, Peter Zijlstra wrote:
> On Thu, Dec 19, 2013 at 06:07:41PM +0100, Ingo Molnar wrote:
> > Likewise, having a barrier before the MONITOR looks sensible as well. 
> 
> I again have to disagree, one would expect monitor to flush all that is
> required to start the monitor -- and it actually does so. As is
> testified by this extra CLFLUSH being called a bug workaround.

SDM states that MONITOR is ordered like a LOAD, and a LOAD cannot pass
a previous STORE to the same address.

That said; there's enough holes in there to swim a titanic through,
seeing how MONITOR stares at an entire cacheline and LOAD/STORE order is
specified on location, whatever that means.