From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932497Ab2BJUjG (ORCPT ); Fri, 10 Feb 2012 15:39:06 -0500 Received: from mail-vw0-f46.google.com ([209.85.212.46]:42912 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755209Ab2BJUjE convert rfc822-to-8bit (ORCPT ); Fri, 10 Feb 2012 15:39:04 -0500 MIME-Version: 1.0 X-Originating-IP: [89.138.49.59] In-Reply-To: <1328905759.25989.57.camel@laptop> References: <1327572121-13673-1-git-send-email-gilad@benyossef.com> <1327591185.2446.102.camel@twins> <20120201170443.GE6731@somewhere.redhat.com> <4F2AAEB9.9070302@tilera.com> <1328899148.25989.38.camel@laptop> <1328905759.25989.57.camel@laptop> Date: Fri, 10 Feb 2012 22:39:02 +0200 Message-ID: Subject: Re: [v7 0/8] Reduce cross CPU IPI interference From: Gilad Ben-Yossef To: Peter Zijlstra Cc: Chris Metcalf , Frederic Weisbecker , linux-kernel@vger.kernel.org, Christoph Lameter , linux-mm@kvack.org, Pekka Enberg , Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , Mel Gorman , Andrew Morton , Alexander Viro , Avi Kivity , Michal Nazarewicz , Kosaki Motohiro , Milton Miller Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 10, 2012 at 10:29 PM, Peter Zijlstra wrote: > On Fri, 2012-02-10 at 22:13 +0200, Gilad Ben-Yossef wrote: >> My current understanding is that if I have a real time task and wish it >> have a deterministic performance time, you should call mlockall() to lock >> the program data and text into physical memory so that  a  less often taken >> branch or access to a new data region will not result in a page fault. >> >> You still have to worry about TLB misses on non hardware page table >> walk architecture, but at least everything is in the  page tables >> >> If there is a better way to do this? I'm always happy to learn new >> ways to do things. :-) > > A rt application usually consists of a lot of non-rt parts and a usually > relatively small rt part. Using mlockall() pins the entire application > into memory, which while on the safe side is very often entirely too > much. > > The alternative method is to only mlock the text and data used by the rt > part. You need to be aware of what text runs in your rt part anyway, > since you need to make sure it is in fact deterministic code. > > One of the ways of achieving this is using a special linker section for > your vetted rt code and mlock()'ing only that text section. > > On thread creation, provide a custom allocated (and mlock()'ed) stack > etc.. > > Basically, if you can't tell a-priory what code is part of your rt part, > you don't have an rt part ;-) > That I can totally agree with. I guess mlockall() is still useful as a kind of hack for lazy people, although if you say that this kind of laziness does not really mix well with real time programming I will tend to agree... :-) Gilad -- Gilad Ben-Yossef Chief Coffee Drinker gilad@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "If you take a class in large-scale robotics, can you end up in a situation where the homework eats your dog?"  -- Jean-Baptiste Queru