Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932520AbVJTUFT (ORCPT ); Thu, 20 Oct 2005 16:05:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932521AbVJTUFT (ORCPT ); Thu, 20 Oct 2005 16:05:19 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:62098 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S932520AbVJTUFR (ORCPT ); Thu, 20 Oct 2005 16:05:17 -0400 Subject: Re: Ktimer / -rt9 (+custom) monotonic_clock going backwards. From: john stultz To: Ingo Molnar Cc: Steven Rostedt , tglx@linutronix.de, linux-kernel@vger.kernel.org In-Reply-To: <20051020193214.GA21613@elte.hu> References: <20051020073416.GA28581@elte.hu> <20051020080107.GA31342@elte.hu> <20051020085955.GB2903@elte.hu> <1129826750.27168.163.camel@cog.beaverton.ibm.com> <20051020193214.GA21613@elte.hu> Content-Type: text/plain Date: Thu, 20 Oct 2005 13:05:13 -0700 Message-Id: <1129838714.27168.181.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1211 Lines: 31 On Thu, 2005-10-20 at 21:32 +0200, Ingo Molnar wrote: > * john stultz wrote: > > > > > John, would this cause any problems to keep cycle_t at s64? > > > > > > I mean at u64. > > > > Performance would be the only concern. It had been a u64 before I > > started optimizing the code a bit. > > no, this is really a bad optimization that causes unrobustness. > Correctness and robustness comes first. It is so easy to cause a > 500-1000msec delay in the kernel, due to a bad driver or anything. The > timekeeping code should not break like that. Eh, its an easy enough change, so I'll put it back to u64. We can revisit it again later if needed. However making sure periodic_hook isn't starved for too long is important for good timekeeping, since ntp and cpufreq adjustments are made at that point. Steven's suggestion of moving it to use ktimers sounds like a good plan, but let me know if you can see any other holes. thanks -john. - 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/