From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Revell Subject: Re: Re: [Jackit-devel] irq handler top half timestamps Date: Fri, 10 Dec 2004 16:01:48 -0500 Message-ID: <1102712509.29919.46.camel@krustophenia.net> References: <200412102051.iBAKphFL012668@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <200412102051.iBAKphFL012668@localhost.localdomain> Sender: alsa-devel-admin@lists.sourceforge.net Errors-To: alsa-devel-admin@lists.sourceforge.net List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , List-Archive: To: Paul Davis Cc: Florian Schmidt , Jaroslav Kysela , Ingo Molnar , jackit-devel@lists.sourceforge.net, alsa-devel List-Id: alsa-devel@alsa-project.org On Fri, 2004-12-10 at 15:51 -0500, Paul Davis wrote: > >Maybe I am not understanding the ALSA code correctly, but I was under > >the impression that ALSA interrupt handlers do not really have a bottom > >half as such, in that they do not schedule any work for later via > >raising a softirq or scheduling a tasklet. They just do it all in the > >top half. It's possible for ALSA to do everything in the top half > >because all you do in an ALSA interrupt handler is call > >snd_pcm_period_elapsed on one or more substreams. For this to work it > >seem like snd_pcm_period_elapsed has to be O(N) and therefore realtime > >safe. > > with ingo's RP patches, every IRQ has a top half and bottom half. the > question is whether the top half calls the bottom half directly or > arranges for it to run in a thread "later". Yeah, exactly. I was speaking in terms of the traditional bottom half/top half model. With Ingo's patches we actually have 3 levels of IRQ context, they effectively add a level above the traditional "top half" which is just a tiny asm routine to mark the IRQ thread runnable (if threaded) or execute the "real" top half directly if nonthreaded. I don't really consider this new level very significant in practice because it's fast and exactly the same for all devices. IOW the snd_pcm_period_elapsed timestamp should be good. I don't think we need to worry about the threaded ALSA IRQ case. Lee ------------------------------------------------------- SF email is sponsored by - The IT Product Guide Read honest & candid reviews on hundreds of IT Products from real users. Discover which products truly live up to the hype. Start reading now. http://productguide.itmanagersjournal.com/