Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1033565AbbKEQ70 (ORCPT ); Thu, 5 Nov 2015 11:59:26 -0500 Received: from g1t6216.austin.hp.com ([15.73.96.123]:36042 "EHLO g1t6216.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030726AbbKEQ7Y (ORCPT ); Thu, 5 Nov 2015 11:59:24 -0500 Message-ID: <563B8AE9.1040000@hpe.com> Date: Thu, 05 Nov 2015 11:59:21 -0500 From: Waiman Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130109 Thunderbird/10.0.12 MIME-Version: 1.0 To: Peter Zijlstra CC: Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , x86@kernel.org, linux-kernel@vger.kernel.org, Scott J Norton , Douglas Hatch , Davidlohr Bueso Subject: Re: [PATCH tip/locking/core v9 4/6] locking/pvqspinlock: Collect slowpath lock statistics References: <1446247597-61863-1-git-send-email-Waiman.Long@hpe.com> <1446247597-61863-5-git-send-email-Waiman.Long@hpe.com> <20151102164040.GV3604@twins.programming.kicks-ass.net> <563B83E9.60909@hpe.com> <20151105164322.GH3604@twins.programming.kicks-ass.net> In-Reply-To: <20151105164322.GH3604@twins.programming.kicks-ass.net> 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: 2079 Lines: 46 On 11/05/2015 11:43 AM, Peter Zijlstra wrote: > On Thu, Nov 05, 2015 at 11:29:29AM -0500, Waiman Long wrote: >> On 11/02/2015 11:40 AM, Peter Zijlstra wrote: >>> On Fri, Oct 30, 2015 at 07:26:35PM -0400, Waiman Long wrote: >>>> This patch enables the accumulation of kicking and waiting related >>>> PV qspinlock statistics when the new QUEUED_LOCK_STAT configuration >>>> option is selected. It also enables the collection of data which >>>> enable us to calculate the kicking and wakeup latencies which have >>>> a heavy dependency on the CPUs being used. >>>> >>>> The statistical counters are per-cpu variables to minimize the >>>> performance overhead in their updates. These counters are exported >>>> via the sysfs filesystem under the /sys/kernel/qlockstat directory. >>>> When the corresponding sysfs files are read, summation and computing >>>> of the required data are then performed. >>> Why did you switch to sysfs? You can create custom debugfs files too. >> I was not aware of that capability. So you mean using debugfs_create_file() >> using custom file_operations. Right? > Yep. > >> That doesn't seem to be easier than >> using sysfs. However, I can use that if you think it is better to use >> debugfs. > Mostly I just wanted to point out that it was possible; you need not > change to sysfs because debugfs lacks the capability. > > But now that you ask, I think debugfs might be the better place, such > statistics (and the proposed CONFIG symbol) are purely for debug > purposes, right? Davidlohr had asked me to use per-cpu counters to reduce performance overhead so that they can be usable in production system. That is another reason why I move to sysfs. BTW, do you have comments on the other patches in the series? I would like to collect all the comments before I renew the series. Cheers, Longman -- 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/