Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756310AbYGFJk5 (ORCPT ); Sun, 6 Jul 2008 05:40:57 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752205AbYGFJks (ORCPT ); Sun, 6 Jul 2008 05:40:48 -0400 Received: from mail-out.m-online.net ([212.18.0.9]:43013 "EHLO mail-out.m-online.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752009AbYGFJkr (ORCPT ); Sun, 6 Jul 2008 05:40:47 -0400 X-Auth-Info: o+lKTsKCUi+6gpu8l6+4UVXrektXcCLn/cdYq+l0jf0= X-Auth-Info: o+lKTsKCUi+6gpu8l6+4UVXrektXcCLn/cdYq+l0jf0= X-Auth-Info: o+lKTsKCUi+6gpu8l6+4UVXrektXcCLn/cdYq+l0jf0= X-Auth-Info: o+lKTsKCUi+6gpu8l6+4UVXrektXcCLn/cdYq+l0jf0= X-Auth-Info: o+lKTsKCUi+6gpu8l6+4UVXrektXcCLn/cdYq+l0jf0= X-Auth-Info: o+lKTsKCUi+6gpu8l6+4UVXrektXcCLn/cdYq+l0jf0= X-Auth-Info: o+lKTsKCUi+6gpu8l6+4UVXrektXcCLn/cdYq+l0jf0= Message-ID: <48709348.6000101@grandegger.com> Date: Sun, 06 Jul 2008 11:41:28 +0200 From: Wolfgang Grandegger User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Steven Rostedt 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? 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> In-Reply-To: X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1202 Lines: 28 Steven Rostedt wrote: > 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. Yep, in 2.6.25.8-rt7 trace_mark() is not used any more, maybe for that reason. Nevertheless, this "bug" kept the latency on my MPC5200 box low. I will try with the old tracer to understand what the real cause of the high latencies is (with CONFIG_RCU_TRACE disabled). Wolfgang. -- 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/