From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Lindgren Subject: Re: [PATCH 5/6] ARM: OMAP2: drop redundant pending write check for gptimer Date: Sun, 7 Dec 2008 12:54:29 -0800 Message-ID: <20081207205428.GA7388@atomide.com> References: <20081205023737.3868.78857.stgit@localhost> <20081205024121.3868.18876.stgit@localhost> <20081207112511.GB1646@flint.arm.linux.org.uk> <13B9B4C6EF24D648824FF11BE8967162036D05AD4C@dlee02.ent.ti.com> <20081207170624.GA17640@flint.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mho-01-bos.mailhop.org ([63.208.196.178]:61940 "EHLO mho-01-bos.mailhop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751471AbYLGUyk (ORCPT ); Sun, 7 Dec 2008 15:54:40 -0500 Content-Disposition: inline In-Reply-To: <20081207170624.GA17640@flint.arm.linux.org.uk> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Russell King - ARM Linux Cc: "Woodruff, Richard" , "linux-arm-kernel@lists.arm.linux.org.uk" , Kevin Hilman , Paul Walmsley , "linux-omap@vger.kernel.org" * Russell King - ARM Linux [081207 09:06]: > On Sun, Dec 07, 2008 at 08:55:54AM -0600, Woodruff, Richard wrote: > > Yes, NOHZ is _poor_ today in respect to needless reprogramming. Code can > > be improved. I have sent Thomas a patch for the same which is in the MM > > tree for a while now. > > When I discussed this problem with Thomas, his reaction was rather > negative due to there being conflicting requirements between this and > ia64. And quite frankly I think that the OMAP behaviour is utter > madness - taking as long as it does to update the timer registers > means that no matter what you do, you _will_ be paying a penalty > for that hardware. Well still the timer code should be optimized for slower systems. The timer should not be reprogrammed during every device interrupt if the change is less than a jiffy. And going through the timer lists is not always needed, so Richard's patch tries to optimize that [1]. > Let's hope that later OMAP designs sanitise the timer hardware so > it doesn't take stupid amounts of time to write to the registers, > posted mode or not. Yeah. Richard has some profiling data showing you how much time is spent doing that, maybe post that again for reference? It's very interesting data. Tony [1] http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.28-rc2/2.6.28-rc2-mm1/broken-out/tick-schedc-suppress-needless-timer-reprogramming.patch