Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261242AbUKWBhp (ORCPT ); Mon, 22 Nov 2004 20:37:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262526AbUKWBha (ORCPT ); Mon, 22 Nov 2004 20:37:30 -0500 Received: from mail.timesys.com ([65.117.135.102]:31915 "EHLO exchange.timesys.com") by vger.kernel.org with ESMTP id S261242AbUKWBg7 (ORCPT ); Mon, 22 Nov 2004 20:36:59 -0500 Message-ID: <41A293B4.8000002@timesys.com> Date: Mon, 22 Nov 2004 20:34:44 -0500 From: john cooper User-Agent: Mozilla Thunderbird 0.8 (X11/20040913) X-Accept-Language: en-us, en MIME-Version: 1.0 To: "Bill Huey (hui)" CC: Esben Nielsen , linux-kernel@vger.kernel.org, Ingo Molnar , john cooper Subject: Re: Priority Inheritance Test (Real-Time Preemption) References: <20041122092302.GA7210@nietzsche.lynx.com> <41A1F4B2.10401@timesys.com> <20041122213054.GB9058@nietzsche.lynx.com> In-Reply-To: <20041122213054.GB9058@nietzsche.lynx.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 23 Nov 2004 01:30:16.0859 (UTC) FILETIME=[FCB956B0:01C4D0FB] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1330 Lines: 38 Bill Huey (hui) wrote: > On Mon, Nov 22, 2004 at 09:16:18AM -0500, john cooper wrote: > >>I'd hazard a guess the reason existing implementations do not >>do this type of dependency-chain closure is the complexity of a >>general approach. Getting correct behavior and scaling on SMP >>require some restrictions of how lock ownership is maintained, >>otherwise fine grained locking is not possible. Another likely > > > What do you mean by that ? Are you talking about strict priority > obedience by the system ? Not quite if I understand your question. I was referring to avoiding having a global lock to synchronize the conglomerate data structure when doing a PI dependency walk. The problem is the lock must be acquired not only in PI scenarios but in any case which may possibly lead to one or affect a concurrent PI in progress. True this global lock is mostly an issue for large count SMP systems. But as witnessed by such voodoo[1] mechanisms as rcu, scalability problems are real at that end of the spectrum. -john [1] in a 'nice' way. -- john.cooper@timesys.com - 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/