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 S1756714AbbEUQCa (ORCPT <rfc822;w@1wt.eu>);
	Thu, 21 May 2015 12:02:30 -0400
Received: from cantor2.suse.de ([195.135.220.15]:59575 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1755942AbbEUQC1 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Thu, 21 May 2015 12:02:27 -0400
Date: Thu, 21 May 2015 18:02:23 +0200
From: Borislav Petkov <bp@suse.de>
To: Huang Rui <ray.huang@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
        Ingo Molnar <mingo@kernel.org>, Len Brown <lenb@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Fengguang Wu <fengguang.wu@intel.com>, Aaron Lu <aaron.lu@intel.com>,
        "Li, Tony" <Tony.Li@amd.com>,
        =?utf-8?B?RnLDqWTDqXJpYw==?= Weisbecker <fweisbec@gmail.com>,
        Andy Lutomirski <luto@amacapital.net>
Subject: Re: [RFC PATCH 2/4] x86, mwaitt: introduce mwaitx idle with a
 configurable timer
Message-ID: <20150521160223.GA23652@pd.tnic>
References: <20150520111120.GA25215@gmail.com>
 <20150520112110.GG3645@pd.tnic>
 <20150520114125.GA31212@gmail.com>
 <alpine.DEB.2.11.1505201518050.4225@nanos>
 <20150520145122.GB10374@gmail.com>
 <20150520165558.24bf2483@lxorguk.ukuu.org.uk>
 <20150520160702.GH3645@pd.tnic>
 <alpine.DEB.2.11.1505202105110.4225@nanos>
 <20150520201553.GI3645@pd.tnic>
 <20150521145632.GC22642@hr-slim.amd.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20150521145632.GC22642@hr-slim.amd.com>
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

On Thu, May 21, 2015 at 10:56:32PM +0800, Huang Rui wrote:
> Looks like good use case. Boris, could we try to implement it?

Andy had some suggestions on how to do it here:

https://lkml.kernel.org/r/555D3629.8080002@kernel.org

which should be doable. Also, you'd probably need to set ECX[0]=0b too,
so that MWAITX doesn't get woken up by interrupts while MWAIT-ing with
interrupts disabled. I.e., this sequence:

cli
rdtsc
shove the computed timeout into ebx
mov $2,%ecx				# this enables the timer and disables IRQs while MWAITing
mwaitx
sti

The NMI argument is a problem though - if and NMI gets you out of
MWAITX, a simple perf tool workload would kill all MWAITX executions.
Which is bad. :-\

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--