From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e39.co.us.ibm.com (e39.co.us.ibm.com [32.97.110.160]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 2D713140084 for ; Sun, 11 May 2014 02:33:34 +1000 (EST) Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 10 May 2014 10:33:32 -0600 Received: from b03cxnp08027.gho.boulder.ibm.com (b03cxnp08027.gho.boulder.ibm.com [9.17.130.19]) by d03dlp01.boulder.ibm.com (Postfix) with ESMTP id 379481FF003D for ; Sat, 10 May 2014 10:33:31 -0600 (MDT) Received: from d03av06.boulder.ibm.com (d03av06.boulder.ibm.com [9.17.195.245]) by b03cxnp08027.gho.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s4AGWegT3080682 for ; Sat, 10 May 2014 18:32:41 +0200 Received: from d03av06.boulder.ibm.com (loopback [127.0.0.1]) by d03av06.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id s4AGbMWM020102 for ; Sat, 10 May 2014 10:37:22 -0600 Date: Sat, 10 May 2014 09:33:28 -0700 From: "Paul E. McKenney" To: Paul Mackerras Subject: Re: [PATCH] powerpc: irq work racing with timer interrupt can result in timer interrupt hang Message-ID: <20140510163328.GA4827@linux.vnet.ibm.com> References: <20140509174712.55fe72d0@kryten> <20140509134113.GP8754@linux.vnet.ibm.com> <20140509215005.GA28239@visitor2.iram.es> <20140509220845.GY8754@linux.vnet.ibm.com> <20140510063337.GA13634@iris.ozlabs.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20140510063337.GA13634@iris.ozlabs.ibm.com> Cc: linuxppc-dev@lists.ozlabs.org, Anton Blanchard Reply-To: paulmck@linux.vnet.ibm.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sat, May 10, 2014 at 04:33:37PM +1000, Paul Mackerras wrote: > On Fri, May 09, 2014 at 03:08:45PM -0700, Paul E. McKenney wrote: > > On Fri, May 09, 2014 at 11:50:05PM +0200, Gabriel Paubert wrote: > > > On Fri, May 09, 2014 at 06:41:13AM -0700, Paul E. McKenney wrote: > > > > On Fri, May 09, 2014 at 05:47:12PM +1000, Anton Blanchard wrote: > > > > > I am seeing an issue where a CPU running perf eventually hangs. > > > > > Traces show timer interrupts happening every 4 seconds even > > > > > when a userspace task is running on the CPU. > > > > > > > > Is this by chance every 4.2 seconds? The reason I ask is that > > > > Paul Clarke and I are seeing an interrupt every 4.2 seconds when > > > > he runs NO_HZ_FULL, and are trying to get rid of it. ;-) > > > > > > Hmmm, it's close to 2^32 nanoseconds, isnt't it suspiscious? > > > > Now that you mention it... ;-) > > > > So you are telling me that we are not succeeding in completely turning > > off the decrementer interrupt? > > There is no way to turn off the decrementer interrupt without turning > off external (device) interrupts. > > On IBM Power CPUs since POWER6, the decrementer runs at 512MHz. If > you set the decrementer to 0x7fffffff it will interrupt in 4.194 > seconds, so that would be what you're seeing. The only way to avoid > the interrupt becoming pending is to keep on setting it to a large > value before it gets to -1. > > If an interrupt every 4.2 seconds is a problem in some applications, > then we need to talk to the Power architects. Thank you for filling me in on this! Might be worth doing just that. Thanx, Paul