From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH RFC 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation Date: Thu, 1 Aug 2013 22:10:18 +0200 Message-ID: <20130801201018.GR3008@twins.programming.kicks-ass.net> References: <1375324631-32868-1-git-send-email-Waiman.Long@hp.com> <1375324631-32868-2-git-send-email-Waiman.Long@hp.com> <20130801094029.GK3008@twins.programming.kicks-ass.net> <51FAA1C3.2050507@hp.com> <51FAA5F8.2070209@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from merlin.infradead.org ([205.233.59.134]:53598 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751595Ab3HAUKj (ORCPT ); Thu, 1 Aug 2013 16:10:39 -0400 Content-Disposition: inline In-Reply-To: <51FAA5F8.2070209@linux.vnet.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Raghavendra K T Cc: Waiman Long , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Arnd Bergmann , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt , Andrew Morton , Richard Weinberger , Catalin Marinas , Greg Kroah-Hartman , Matt Fleming , Herbert Xu , Akinobu Mita , Rusty Russell , Michel Lespinasse , Andi Kleen , Rik van Riel , "Paul E. McKenney" , Linus Torvalds , George Spelvin , Harvey Harrison On Thu, Aug 01, 2013 at 11:46:24PM +0530, Raghavendra K T wrote: > On 08/01/2013 11:28 PM, Waiman Long wrote: > >On 08/01/2013 05:40 AM, Peter Zijlstra wrote: > >>On Wed, Jul 31, 2013 at 10:37:10PM -0400, Waiman Long wrote: > >> > [...] > >> > >>>+ */ > >>>+ for (qn_idx = 1; qn_idx< MAX_QNODES; qn_idx++) { > >>>+ if (!node[qn_idx].used) > >>>+ break; > >> } > >> > >>>+ if (unlikely(qn_idx == MAX_QNODES)) { > >>>+ /* > >>>+ * This shouldn't happen, print a warning message > >>>+ *& busy spinning on the lock. > >>>+ */ > >>>+ pr_warn("qspinlock: queue node table exhausted at " > >>>+ "cpu %d!\n", cpu_nr); > >>This could make your machine die hard.. not all contexts can printk(). > > > >Do you have any suggestion? I could skip the warning and silently do the > >busy spinning. I just want some way to notify the user of this rare event. > > We have used debugfs in pv-spinlock to avoid that since printk uses > spinlock again. may be it will help to profile many other parts of > code too. I always use early_printk(), but that requires you set up your serial console properly and joe-user won't have done that. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from merlin.infradead.org ([205.233.59.134]:53598 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751595Ab3HAUKj (ORCPT ); Thu, 1 Aug 2013 16:10:39 -0400 Date: Thu, 1 Aug 2013 22:10:18 +0200 From: Peter Zijlstra Subject: Re: [PATCH RFC 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation Message-ID: <20130801201018.GR3008@twins.programming.kicks-ass.net> References: <1375324631-32868-1-git-send-email-Waiman.Long@hp.com> <1375324631-32868-2-git-send-email-Waiman.Long@hp.com> <20130801094029.GK3008@twins.programming.kicks-ass.net> <51FAA1C3.2050507@hp.com> <51FAA5F8.2070209@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <51FAA5F8.2070209@linux.vnet.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Raghavendra K T Cc: Waiman Long , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Arnd Bergmann , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt , Andrew Morton , Richard Weinberger , Catalin Marinas , Greg Kroah-Hartman , Matt Fleming , Herbert Xu , Akinobu Mita , Rusty Russell , Michel Lespinasse , Andi Kleen , Rik van Riel , "Paul E. McKenney" , Linus Torvalds , George Spelvin , Harvey Harrison , "Chandramouleeswaran, Aswin" , "Norton, Scott J" Message-ID: <20130801201018.HI6JOB-Nk_WSwJn8ndWoORya0f7vKuZgJNAGENwR6zU@z> On Thu, Aug 01, 2013 at 11:46:24PM +0530, Raghavendra K T wrote: > On 08/01/2013 11:28 PM, Waiman Long wrote: > >On 08/01/2013 05:40 AM, Peter Zijlstra wrote: > >>On Wed, Jul 31, 2013 at 10:37:10PM -0400, Waiman Long wrote: > >> > [...] > >> > >>>+ */ > >>>+ for (qn_idx = 1; qn_idx< MAX_QNODES; qn_idx++) { > >>>+ if (!node[qn_idx].used) > >>>+ break; > >> } > >> > >>>+ if (unlikely(qn_idx == MAX_QNODES)) { > >>>+ /* > >>>+ * This shouldn't happen, print a warning message > >>>+ *& busy spinning on the lock. > >>>+ */ > >>>+ pr_warn("qspinlock: queue node table exhausted at " > >>>+ "cpu %d!\n", cpu_nr); > >>This could make your machine die hard.. not all contexts can printk(). > > > >Do you have any suggestion? I could skip the warning and silently do the > >busy spinning. I just want some way to notify the user of this rare event. > > We have used debugfs in pv-spinlock to avoid that since printk uses > spinlock again. may be it will help to profile many other parts of > code too. I always use early_printk(), but that requires you set up your serial console properly and joe-user won't have done that.