Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S270824AbUJUU5P (ORCPT ); Thu, 21 Oct 2004 16:57:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S270838AbUJUUms (ORCPT ); Thu, 21 Oct 2004 16:42:48 -0400 Received: from smtp.Lynuxworks.com ([207.21.185.24]:2820 "EHLO smtp.lynuxworks.com") by vger.kernel.org with ESMTP id S270937AbUJUUiy (ORCPT ); Thu, 21 Oct 2004 16:38:54 -0400 Date: Thu, 21 Oct 2004 13:38:21 -0700 To: Jens Axboe Cc: Bill Huey , Thomas Gleixner , Rui Nuno Capela , Ingo Molnar , LKML , Lee Revell , mark_h_johnson@raytheon.com, "K.R. Foley" , Adam Heath , Florian Schmidt , Michal Schmidt , Fernando Pablo Lopez-Lezcano Subject: Re: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U8 Message-ID: <20041021203821.GA24628@nietzsche.lynx.com> References: <20041020094508.GA29080@elte.hu> <30690.195.245.190.93.1098349976.squirrel@195.245.190.93> <1098350190.26758.24.camel@thomas> <20041021095344.GA10531@suse.de> <1098352441.26758.30.camel@thomas> <20041021101103.GC10531@suse.de> <20041021195842.GA23864@nietzsche.lynx.com> <20041021201443.GF32465@suse.de> <20041021202422.GA24555@nietzsche.lynx.com> <20041021203350.GK32465@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20041021203350.GK32465@suse.de> User-Agent: Mutt/1.5.6+20040907i From: Bill Huey (hui) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1533 Lines: 30 On Thu, Oct 21, 2004 at 10:33:50PM +0200, Jens Axboe wrote: > On Thu, Oct 21 2004, Bill Huey wrote: > > You use a semaphore to protect data, a completion isn't protecting data > > but preserving a certain kind of wait ordering in the code. The > > possibility of overloading the current mutex_t for PI makes for a conceptual > > mismatch when used in this case since having a kind of priority for > > completions is a bit odd. It's better to flat out use a completion > > instead, IMO. > > Linux semaphores (being counted) have always been a fine fit for things > like the loop use, where you get to down it 10 times because you have 10 > items pending. I know this isn't the traditional mutex and that it > doesn't protect data as such, but is was never abuse. It isn't overload. > Doing it with a traditional mutex (I'm assuming this is what mutex_t is > in Ingos tree) would be overload and a bad idea, indeed. Well, this is something that's got to be considered by the larger Linux community and whether these conventions are to be kept or removed. It's a larger issue than what can be address in Ingo's preemption patch, but with inevitable need for something like this in the kernel (hard RT) it's really unavoidable collision. IMO, it's got to go, which is a nasty change. bill - 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/