linux-kernel - Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

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Date:	Wed, 20 Nov 2013 08:24:47 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>
CC:	lenb@...nel.org, rjw@...ysocki.net, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, shaohua.li@...el.com,
	rui.zhang@...el.com, Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>, hpa@...or.com
Subject: Re: [PATCH] x86, acpi, idle: Restructure the mwait idle routines

On 11/20/2013 2:58 AM, Peter Zijlstra wrote:
> On Wed, Nov 20, 2013 at 11:28:03AM +0100, Peter Zijlstra wrote:
>> On Tue, Nov 19, 2013 at 01:06:30PM -0800, Jacob Pan wrote:
>>> I applied this patch on top of upstream kernel (801a760) and found out
>>> my machine completely failed to enter idle when nothing is running.
>>> turbostate shows 100% C0. ftrace shows kernel coming in and out of idle
>>> frequently.
>>>
>>> Both ACPI idle and intel_idle behaves the same way. I have to do the
>>> following change to allow entering C-states again.
>
>> That doesn't make any sense; current_set_polling_and_test() returns the
>> same thing need_resched() does.
>>
>> But you're right, intel_idle resides 100% in C0 and acpi_idle has 100%
>> C1 residency... most weird.
>
> So pretty silly actually; you cannot do a store (any store) in between
> monitor and mwait.

you can
just not to the cacheline you are watching (or things that alias with that)

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