Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754752AbaDKDwl (ORCPT <rfc822;w@1wt.eu>);
	Thu, 10 Apr 2014 23:52:41 -0400
Received: from mail-ee0-f47.google.com ([74.125.83.47]:49670 "EHLO
	mail-ee0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751938AbaDKDwj (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 10 Apr 2014 23:52:39 -0400
Message-ID: <1397188356.5139.33.camel@marge.simpson.net>
Subject: Re: [RFC PATCH RT] rwsem: The return of multi-reader PI rwsems
From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
        linux-rt-users <linux-rt-users@vger.kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Clark Williams <williams@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>
Date: Fri, 11 Apr 2014 05:52:36 +0200
In-Reply-To: <20140410232542.23ee9920@gandalf.local.home>
References: <20140409151922.5fa5d999@gandalf.local.home>
	 <1397139510.5137.92.camel@marge.simpson.net>
	 <1397140123.5137.99.camel@marge.simpson.net>
	 <1397184626.5139.24.camel@marge.simpson.net>
	 <20140410232542.23ee9920@gandalf.local.home>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.2.3 
Content-Transfer-Encoding: 7bit
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, 2014-04-10 at 23:25 -0400, Steven Rostedt wrote: 
> On Fri, 11 Apr 2014 04:50:26 +0200
> Mike Galbraith <umgwanakikbuti@gmail.com> wrote:
> 
> > Oh, there was another useful bit. 
> > 
> > 3.12.17-rt25       403991     384216     377786
> >                    405466     394011     392850
> > 
> > 3.12.17-nopreempt  109049     186133     118766  !?!.. ew, TTWU_QUEUE
> >                    350385     318786     367336  !TTWU_QUEUE
> >                    326009     356939     378215  !TTWU_QUEUE
> > 
> > IPI == low-pass filter.
> 
> I'm sorry, but I don't have the foggiest clue to what the above means.

It means..

# Overhead                                                                                                                                                                                   Symbol
# ........  .......................................................................................................................................................................................
#
    17.33%  [k] native_write_msr_safe
            |
            |--88.45%-- __x2apic_send_IPI_mask
            |          |
            |          |--97.89%-- try_to_wake_up
            |          |          |
            |          |          |--99.91%-- wake_futex
            |          |          |          |
            |          |          |          |--99.77%-- futex_wake_op
            |          |          |          |          do_futex
            |          |          |          |          sys_futex
            |          |          |          |          system_call_fastpath

..wakeup frequency is restricted by the IPI.

	-Mike

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/