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 S1752102AbcA0EPa (ORCPT <rfc822;w@1wt.eu>);
	Tue, 26 Jan 2016 23:15:30 -0500
Received: from mail-wm0-f51.google.com ([74.125.82.51]:34547 "EHLO
	mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751021AbcA0EP2 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 26 Jan 2016 23:15:28 -0500
Message-ID: <1453868124.3622.31.camel@gmail.com>
Subject: Re: fast path cycle muncher (vmstat: make vmstat_updater deferrable
 again and shut down on idle)
From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>
Date: Wed, 27 Jan 2016 05:15:24 +0100
In-Reply-To: <1453864347.3622.10.camel@gmail.com>
References: <alpine.DEB.2.20.1601210941540.7063@east.gentwo.org>
	 <20160121165148.GF29520@dhcp22.suse.cz>
	 <alpine.DEB.2.20.1601211130580.7741@east.gentwo.org>
	 <20160122140418.GB19465@dhcp22.suse.cz>
	 <alpine.DEB.2.20.1601220950290.17929@east.gentwo.org>
	 <20160122161201.GC19465@dhcp22.suse.cz>
	 <alpine.DEB.2.20.1601221046020.17984@east.gentwo.org>
	 <1453566115.3529.8.camel@gmail.com> <20160125174224.GH23934@dhcp22.suse.cz>
	 <alpine.DEB.2.20.1601251152290.19487@east.gentwo.org>
	 <20160125201319.GA19020@dhcp22.suse.cz>
	 <alpine.DEB.2.20.1601261022140.27957@east.gentwo.org>
	 <1453833078.3534.59.camel@gmail.com>
	 <alpine.DEB.2.20.1601261233400.2181@east.gentwo.org>
	 <1453833939.3534.68.camel@gmail.com>
	 <alpine.DEB.2.20.1601261317410.4024@east.gentwo.org>
	 <1453864347.3622.10.camel@gmail.com>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.16.5 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, 2016-01-27 at 04:12 +0100, Mike Galbraith wrote:
> Good morning,
> 
> On Tue, 2016-01-26 at 13:20 -0600, Christoph Lameter wrote:
> > On Tue, 26 Jan 2016, Mike Galbraith wrote:
> > 
> > > > The system going idle is a fastpath. Mind boogling.
> > > 
> > > Hohum, noted.  Now what about those cycles, and the sleeping lock you
> > > injected for -rt?
> > 
> > Since we (the NOHZ people) care mostly about NOHZ then lets restrict
> > that to the NOHZ mode. Then it should not affect your load.
> 
> Tons of folks do have NO_HZ enabled (including me).  Isn't there a spot
> somewhere in NO_HZ_FULL code where it can take up residence?  (one with
> a tad lower maximum call frequency would be good, a nohz_full cpu isn't
> necessarily being used for pure compute exclusively)

I forgot to mention that the spot you picked is called with irqs
disabled.

> > Subject: Move quiet_vmstat() to NOHZ code
> > 
> > quiet_vmstat() seems to cause regressions for some load because
> > the cpu going idle is a "fastpath". Mind boogling. Strange claim.
> > If the system goes idle then it has nothing to do after all

Hm, seems I also forgot to say "Hohum, noted..." again.

	-Mike