From mboxrd@z Thu Jan 1 00:00:00 1970 From: Raghavendra K T Subject: Re: [PATCH RFC 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation Date: Thu, 01 Aug 2013 23:46:24 +0530 Message-ID: <51FAA5F8.2070209@linux.vnet.ibm.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51FAA1C3.2050507@hp.com> Sender: linux-kernel-owner@vger.kernel.org To: Waiman Long Cc: Peter Zijlstra , 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 List-Id: linux-arch.vger.kernel.org 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. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e23smtp01.au.ibm.com ([202.81.31.143]:51950 "EHLO e23smtp01.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752852Ab3HASKN (ORCPT ); Thu, 1 Aug 2013 14:10:13 -0400 Received: from /spool/local by e23smtp01.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 2 Aug 2013 04:00:16 +1000 Message-ID: <51FAA5F8.2070209@linux.vnet.ibm.com> Date: Thu, 01 Aug 2013 23:46:24 +0530 From: Raghavendra K T MIME-Version: 1.0 Subject: Re: [PATCH RFC 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation 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> In-Reply-To: <51FAA1C3.2050507@hp.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Waiman Long Cc: Peter Zijlstra , 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: <20130801181624.mmk73D9lWeWGkxt99NJJHqUtzkQwd70ym2W0Ip6WVf0@z> 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.