From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763025AbYBMGXT (ORCPT ); Wed, 13 Feb 2008 01:23:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752823AbYBMGXJ (ORCPT ); Wed, 13 Feb 2008 01:23:09 -0500 Received: from smtp104.mail.mud.yahoo.com ([209.191.85.214]:48536 "HELO smtp104.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752600AbYBMGXI (ORCPT ); Wed, 13 Feb 2008 01:23:08 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:X-Yahoo-Newman-Property:From:To:Subject:Date:User-Agent:Cc:References:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding:Content-Disposition:Message-Id; b=lK8uxOHZBH9PIpRL9w8vChZXmVkQV/dPnbAjf+KBdcA3+UX6ZBT9Tf/w/ydl50n/guXJ1RRUmqpnP1/6Z+aMmsaFipCyMdiFxJVPa3pdHzTfA6EDRY1latLp/eUriptPgEuM+twQsFZ7PgworxwFYMOSaHA5y5Fcbx6hNDxiOxc= ; X-YMail-OSG: h_mt79IVM1nbCfesTPQX6MfgDZPL5nNhh2pfuqxXRTKqdbH94PpIVbs6VS6Ifg8uyBTYJmb6Kw-- X-Yahoo-Newman-Property: ymail-3 From: Nick Piggin To: Max Krasnyansky Subject: Re: [git pull for -mm] CPU isolation extensions (updated2) Date: Wed, 13 Feb 2008 17:22:50 +1100 User-Agent: KMail/1.9.5 Cc: David Miller , akpm@linux-foundation.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, mingo@elte.hu, pj@sgi.com, a.p.zijlstra@chello.nl, gregkh@suse.de, rusty@rustcorp.com.au References: <47B11C45.6060408@qualcomm.com> <200802131511.28643.nickpiggin@yahoo.com.au> <47B288E4.2080403@qualcomm.com> In-Reply-To: <47B288E4.2080403@qualcomm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200802131722.51117.nickpiggin@yahoo.com.au> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday 13 February 2008 17:06, Max Krasnyansky wrote: > Nick Piggin wrote: > > But don't let me dissuade you from making these good improvements > > to Linux as well :) Just that it isn't really going to be hard-rt > > in general. > > Actually that's the cool thing about CPU isolation. Get rid of all latency > sources from the CPU(s) and you get youself as hard-RT as it gets. Hmm, maybe. Removing all sources of latency from the CPU kind of implies that you have to audit the whole kernel for source of latency. > I mean I _already_ have multi-core hard-RT systems that show ~1.2 usec > worst case and ~200nsec average latency. I do not even need Adeos/Xenomai > or Preemp-RT just a few very small patches. And it can be used for non RT > stuff too. OK, but you then are very restricted in what you can do, and easily can break it especially if you run any userspace on that CPU. If you just run a kernel module that, after setup, doesn't use any other kernel resources except interrupt handling, then you might be OK (depending on whether even interrupt handling can run into contended locks)... If you started doing very much more, then you can easily run into trouble.