Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261592AbVDTMmA (ORCPT ); Wed, 20 Apr 2005 08:42:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261597AbVDTMmA (ORCPT ); Wed, 20 Apr 2005 08:42:00 -0400 Received: from ns2.suse.de ([195.135.220.15]:58563 "EHLO mx2.suse.de") by vger.kernel.org with ESMTP id S261592AbVDTMlz (ORCPT ); Wed, 20 Apr 2005 08:41:55 -0400 Message-ID: <42664A0E.3050808@suse.de> Date: Wed, 20 Apr 2005 14:24:46 +0200 From: Thomas Renninger User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.7.5) Gecko/20050317 X-Accept-Language: de, en-us, en MIME-Version: 1.0 To: Dominik Brodowski Cc: Tony Lindgren , Frank Sorenson , linux-kernel@vger.kernel.org, Benjamin Herrenschmidt , Pavel Machek , Arjan van de Ven , Martin Schwidefsky , Andrea Arcangeli , George Anzinger , Thomas Gleixner , john stultz , Zwane Mwaikambo , Lee Revell , ML ACPI-devel , Bodo Bauer , Andi Kleen Subject: Re: [PATCH] Updated: Dynamic Tick version 050408-1 - C-state measures References: <4255A7AF.8050802@tuxrocks.com> <4255B247.4080906@tuxrocks.com> <20050408062537.GB4477@atomide.com> <20050408075001.GC4477@atomide.com> <42564584.4080606@tuxrocks.com> <42566C22.4040509@suse.de> <20050408115535.GI4477@atomide.com> <42651C38.6090807@suse.de> <20050419152723.GA9509@isilmar.linta.de> <42657222.5080601@suse.de> <20050420114433.GA28362@isilmar.linta.de> In-Reply-To: <20050420114433.GA28362@isilmar.linta.de> X-Enigmail-Version: 0.90.1.0 X-Enigmail-Supports: pgp-inline, pgp-mime Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3805 Lines: 77 Dominik Brodowski wrote: > On Tue, Apr 19, 2005 at 11:03:30PM +0200, Thomas Renninger wrote: >>>"All" we need to do is to update the "diff". Without dynamic ticks, if the >>>idle loop didn't get called each jiffy, it was a big hint that there was so >>>much activity in between, and if there is activity, there is most likely >>>also bus master activity, or at least more work to do, so interrupt activity >>>is likely. Therefore we assume there was bm_activity even if there was none. >>> >>If I understand this right you want at least wait 32 (or whatever value) ms if there was bm activity, >>before it is allowed to trigger C3/C4? > > That's the theory of operation of the current algorithm. I think that we > should do that small change to the current algorithm which allows us to keep > C3/C4 working with dyn-idle first, and then think of a very small abstraction > layer to test different idle algroithms, and -- possibly -- use different > ones for different usages. > >>I think the problem is (at least I made the experience with this particular >>machine) that bm activity comes very often and regularly (each 30-150ms?). >> >>I think the approach to directly adjust the latency to a deeper sleep state if the >>average bus master and OS activity is low is very efficient. >> >>Because I don't consider whether there was bm_activity the last ms, I only >>consider the average, it seems to happen that I try to trigger >>C3/C4 when there is just something copied and some bm active ?!? > > I don't think that this is perfect behaviour: if the system is idle, and > there is _currently_ bus master activity, the CPU should be put into C1 or > C2 type sleep. If you select C3 and actually enter it, you're risking > DMA issues, AFAICS. > On my system triggering C3/C4 is just ignored (sleep_ticks < 0). These ignorings (C3/C4 failures) seem to directly depend on how much bm_activity there actually is. With the current method (wait at least 30 ms if there was bm activity before triggering C3/C4) these failures never happened. As mentioned using bm_promotion_ms you can lower the failures, but never reach zero. If these failures lead to system freezes on other systems, my next sentence is valid (I meant my patch). >>The patch is useless if these failures end up in system freezes on >>other machines... > > I know that my patch is useless in its current form, but I wanted to share > it as a different way of doing things. > >>The problem with the old approach is, that after (doesn't matter C1-Cx) >>sleep and dyn_idle_tick, the chance to wake up because of bm activity is >>very likely. >>You enter idle() again -> there was bm_activity -> C2. Wake up after e.g. >>50ms, because of bm_activity again (bm_sts bit set) -> stay in C2, wake up >>after 40ms -> bm activity... You only have the chance to get into deeper >>states if the sleeps are interrupted by an interrupt, not bm activity. > > That's a side-effect, indeed. However: if there _is_ bus master activity, we > must not enter C3, AFAICS. > What about a mixed approach: only reprogram timer if you want to go to deeper sleeping states (C3-Cx) when bm activity comes in place? It's the only way you can say: the last xy ms there was no bm activity (use bm_history), now it's safe to sleep and also be efficient: don't sleep forever in C1/C2 -> bm_sts bit will probably be set afterwards and you need to wait another xy ms in C1/C2 -> endless loop ... Like that the timer is only disabled where it is really useful, on C3-Cx machines (or are there other cases?). Thomas - 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/