Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264644AbUKAOew (ORCPT ); Mon, 1 Nov 2004 09:34:52 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262073AbUKAOeu (ORCPT ); Mon, 1 Nov 2004 09:34:50 -0500 Received: from mx1.elte.hu ([157.181.1.137]:45972 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S265257AbUKAO3k (ORCPT ); Mon, 1 Nov 2004 09:29:40 -0500 Date: Mon, 1 Nov 2004 15:30:49 +0100 From: Ingo Molnar To: Paul Davis Cc: Florian Schmidt , Lee Revell , Thomas Gleixner , LKML , mark_h_johnson@raytheon.com, Bill Huey , Adam Heath , Michal Schmidt , Fernando Pablo Lopez-Lezcano , Karsten Wiese , jackit-devel , Rui Nuno Capela , "K.R. Foley" Subject: Re: [Fwd: Re: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0.4] Message-ID: <20041101143049.GA22221@elte.hu> References: <20041101134235.GA18009@elte.hu> <200411011354.iA1Dsleg008831@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200411011354.iA1Dsleg008831@localhost.localdomain> User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1355 Lines: 36 * Paul Davis wrote: > > > >* Florian Schmidt wrote: > > > >> new max. jitter: 4.3% (41 usec) > >> new max. jitter: 4.9% (47 usec) > > > >a couple of conceptual questions: why does rtc_wakeup poll() on > >/dev/rtc? Shouldnt a read() be enough? > > i suggested to florian that it should model jackd's behaviour as > closely as possible. because jackd requires duplex operation, using > just read/write doesn't work. ok - but i think there should at least be an option to turn the poll()-ing off. To showcase the best-possible wakeup latency offered by the kernel :-) poll() is quite complex and with a good number of locks in the path the maximum latency increases accordingly. btw., couldnt jackd use a separate input and output thread (of identical priority), to be purely read()/write() based? This method should also solve the priority problems of poll(): the thread woken up later will do the work later. (hence the _earlier_ interrupt source will be handled first.) With poll() how do you tell which fd needs attention first, if both are set? Ingo - 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/