From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752688AbbETLlb (ORCPT <rfc822;w@1wt.eu>);
	Wed, 20 May 2015 07:41:31 -0400
Received: from mail-wi0-f174.google.com ([209.85.212.174]:34363 "EHLO
	mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751504AbbETLl3 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 20 May 2015 07:41:29 -0400
Date: Wed, 20 May 2015 13:41:25 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@suse.de>
Cc: Huang Rui <ray.huang@amd.com>, Len Brown <lenb@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Fengguang Wu <fengguang.wu@intel.com>,
        Aaron Lu <aaron.lu@intel.com>, Tony Li <tony.li@amd.com>,
        =?iso-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>
Subject: Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a
 configurable timer
Message-ID: <20150520114125.GA31212@gmail.com>
References: <1432022472-2224-1-git-send-email-ray.huang@amd.com>
 <1432022472-2224-3-git-send-email-ray.huang@amd.com>
 <20150519113121.GD4819@pd.tnic>
 <20150520085520.GA8566@gmail.com>
 <20150520091213.GA3645@pd.tnic>
 <20150520102258.GA21245@gmail.com>
 <20150520105032.GD3645@pd.tnic>
 <20150520111120.GA25215@gmail.com>
 <20150520112110.GG3645@pd.tnic>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150520112110.GG3645@pd.tnic>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


* Borislav Petkov <bp@suse.de> wrote:

> On Wed, May 20, 2015 at 01:11:20PM +0200, Ingo Molnar wrote:
> >   - MWAITX takes a 'timeout' parameter, but otherwise behaves exactly 
> >     like MWAIT: i.e. once idle it won't exit idle on its own
> 
> Let me quote the commit message:
> 
> "MWAITT, another name is MWAITX (MWAIT with extensions), has a
> configurable timer that causes MWAITX to exit on expiration."

Ah. A useful skill that is, being able to read.

> You need to set the second bit in ECX to enable the timer.
> 
> I guess if you don't, then you get normal MWAIT but then you don't 
> need the timeout either...

Yeah.

So if it's a true timeout then we could use it to implement irq-less 
timers: that's actually pretty useful, because it could be faster than 
getting a local APIC timer irq, etc.

Thanks,

	Ingo