Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756579AbYGFAmy (ORCPT ); Sat, 5 Jul 2008 20:42:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753305AbYGFAmq (ORCPT ); Sat, 5 Jul 2008 20:42:46 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.123]:41703 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753174AbYGFAmp (ORCPT ); Sat, 5 Jul 2008 20:42:45 -0400 Date: Sat, 5 Jul 2008 20:42:44 -0400 (EDT) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Wolfgang Grandegger cc: "Paul E. McKenney" , Luotao Fu , LKML , RT , Ingo Molnar , Thomas Gleixner Subject: Re: 2.6.24-rc8-rt1: Strange latencies on mpc5200 powerpc - RCU issue? In-Reply-To: <486B607F.9040903@grandegger.com> Message-ID: References: <47976D06.1010900@grandegger.com> <479DF0A1.3000906@pengutronix.de> <479DF711.5090406@grandegger.com> <479F186A.4020004@pengutronix.de> <479F2C3C.1020203@grandegger.com> <20080130010716.GB16069@linux.vnet.ibm.com> <47A032E9.4080105@grandegger.com> <20080130102255.GA24890@linux.vnet.ibm.com> <47A0552D.20605@grandegger.com> <20080130105715.GE24890@linux.vnet.ibm.com> <20080130111559.GC20089@pengutronix.de> <486A3EBB.6030905@grandegger.com> <486A573E.60107@grandegger.com> <486B607F.9040903@grandegger.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 892 Lines: 25 On Wed, 2 Jul 2008, Wolfgang Grandegger wrote: > > I removed all "likely" and "unlikely" macros, but the latencies did not > improve. Then I added > > preempt_disable(); > preempt_enable(); > > at the two locations mentioned above, like trace_mark() does, and > disabled CONFIG_RCU_TRACE. That helped to keep the latencies low, and it > did for 2.6.25.8-rt7 as well. As I see it, adding preemption points seem > to prevent high latencies. This to me sounds like we have preempt_enable_noresched someplace that shouldn't. In otherwords, we enabled preemption without checking if preemption is needed, which is a serious bug in -rt. -- Steve -- 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/