Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261606AbUJXVJ0 (ORCPT ); Sun, 24 Oct 2004 17:09:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261659AbUJXVJ0 (ORCPT ); Sun, 24 Oct 2004 17:09:26 -0400 Received: from smtp.mailbox.co.uk ([195.82.125.32]:58034 "EHLO smtp.mailbox.co.uk") by vger.kernel.org with ESMTP id S261606AbUJXVIz (ORCPT ); Sun, 24 Oct 2004 17:08:55 -0400 Message-ID: <417C19D5.7050802@jonmasters.org> Date: Sun, 24 Oct 2004 22:08:37 +0100 From: Jon Masters Organization: World Organi[sz]ation Of Broken Dreams User-Agent: Mozilla Thunderbird 0.8 (X11/20040918) X-Accept-Language: en-us, en MIME-Version: 1.0 To: paulmck@us.ibm.com CC: Thomas Gleixner , LKML , Ingo Molnar , karim@opersys.com Subject: Re: [RFC][PATCH] Restricted hard realtime References: <20041023194721.GB1268@us.ibm.com> <1098562921.3306.182.camel@thomas> <20041023212421.GF1267@us.ibm.com> <35fb2e5904102315066c6892aa@mail.gmail.com> <20041024153204.GA1262@us.ibm.com> In-Reply-To: <20041024153204.GA1262@us.ibm.com> X-Enigmail-Version: 0.86.1.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-MailScanner: Found to be clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3731 Lines: 81 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Paul E. McKenney wrote: | Thank you for the background! It has been quite some time since I | did significant embedded work. Let's just say that I am glad that | "embedded CPU" no longer means "8-bit CPU"! ;-) Oh it still does, but those cores tend to get farmed out for PSU controll or some specific subsystem unless you're "deeply embedded". jcm>> Talk to smartphone manufacturers who currently have dual ARM jcm>> core designs, one running Linux and the other running an RTOS jcm>> for the GSM and phone stuff, and they'll say they actually jcm>> want to reduce the design complexity down to a single core. jcm>> Talking to people suggests that multicore designs are good jcm>> in certain situations (such as in the case above), but in jcm>> general people aren't yet going to respond to your way of jcm>> doing realtime :-) Yes you do have only one OS in there, jcm>> maybe that would change opinion, but we're not quite at the jcm>> point where everything is multicore so you're not going to jcm>> convince the masses. | Good points. Suppose there was a way to get the hard realtime benefits | using a slight elaboration of this approach that worked on single-core, | single-threaded CPUs? Would that be of interest? I dunno. It might. I think the trouble is that you'll need to convince people who think they want single core designs that it's not a must. Although within a little time it'll increasingly be the case that one has additional cores whether one wants them or not, that's not just yet even now. Someone will doubtlessly disagree. | if you are going for the ultimate in response time, you have | no choice but to run hand-coded assembly language on bare metal (though | optimizing compilers are improving, so maybe it will soon be hand-coded | C on bare metal). Nah. The guys I work with have enough trouble making things time nicely with precisely coded sequences accounting for every available T state. | If you are using your computer to digitally modulate | and synthesize a USA FM radio signal In this case it's large magnets and probes, but yes. Same concept. | So, I guess the question is whether 100-microsecond restricted hard | realtime support in Linux is worth the effort. Some of the folks I work with think not. I'm not sure yet - many people seem to be of the opinion that it's not worth it, but we're told that the Smartphone guys and others without throwaway cores (or to simplify a design somewhat) really want this. Incidentally, it looks like they'll be about a bazzion cores in this particular FPGA range before long, so it'll become increasingly fun finding things for them to do. | So, again, if there was a way to make this approach work on | single-threaded single core CPUs, would that be of interest? I guess it would. But then we've just had a slew of RT implementations crawl out of the woodwork and wave at us over the past few weeks and there are three other major RT implementations which combine Linux with a Microkernel or other external support (RTLinux, RTAI, KURT, etc.). Perhaps it's worth working on one of the Linux patch projects (Monta/Ingo/etc.) rather than going all out to implement it all again. Jon. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.2 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://enigmail.mozdev.org iD8DBQFBfBnUeTyyexZHHxERAo90AKCTgK8ZZCq4Lqw+a1VHFzhtKOO22ACfQy7E hwuQzo04bIlxJy5b1VjGA+E= =4omH -----END PGP SIGNATURE----- - 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/