From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757478AbbGUAlP (ORCPT ); Mon, 20 Jul 2015 20:41:15 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:33229 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756952AbbGUAlK (ORCPT ); Mon, 20 Jul 2015 20:41:10 -0400 X-Helo: d03dlp02.boulder.ibm.com X-MailFrom: paulmck@linux.vnet.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Date: Mon, 20 Jul 2015 17:41:04 -0700 From: "Paul E. McKenney" To: Joe Perches Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, Andy Whitcroft Subject: Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods Message-ID: <20150721004104.GN3717@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20150717221949.GA12304@linux.vnet.ibm.com> <1437171616-13832-1-git-send-email-paulmck@linux.vnet.ibm.com> <1437171616-13832-15-git-send-email-paulmck@linux.vnet.ibm.com> <1437172674.2495.60.camel@perches.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1437172674.2495.60.camel@perches.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15072100-0005-0000-0000-000015C51E46 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 17, 2015 at 03:37:54PM -0700, Joe Perches wrote: > On Fri, 2015-07-17 at 15:20 -0700, Paul E. McKenney wrote: > > The synchronize_rcu_expedited() and synchronize_sched_expedited() > > expedited-grace-period primitives induce OS jitter, which can degrade > > real-time response. This commit therefore adds a checkpatch.pl warning > > on any patch adding them. > [] > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl > [] > > +# Check for expedited grace periods that interrupt non-idle non-nohz > > +# online CPUs. These expedited can therefore degrade real-time response > > +# if used carelessly, and should be avoided where not absolutely > > +# needed. It is always OK to use synchronize_rcu_expedited() and > > +# synchronize_sched_expedited() at boot time (before real-time applications > > +# start) and in error situations where real-time response is compromised in > > +# any case. Note that synchronize_srcu_expedited() does -not- interrupt > > +# other CPUs, so don't warn on uses of synchronize_srcu_expedited(). > > +# Of course, nothing comes for free, and srcu_read_lock() and > > +# srcu_read_unlock() do contain full memory barriers in payment for > > +# synchronize_srcu_expedited() non-interruption properties. > > + if ($line =~ /\b(synchronize_rcu_expedited|synchronize_sched_expedited)\(/) { > > It'd be faster perl without capture groups: > > if ($line =~ /\b(?:synchronize_(?:rcu|sched)_expedited)\s*\(/) { Fair enough, but this pattern is used rather heavily in this script, and I don't trust my perl enough to want to create a new pattern. I see a couple of possible ways forward: 1. I hand this patch off to you, and you update it as you deem fit. 2. I push the patch as is (after the fix below) and you update checkpatch as a whole to use the more efficient code. How would you like to proceed? > > + WARN("EXPEDITED_RCU_GRACE_PERIOD", > > + "expedited RCU grace periods should be avoided in cases where they can degrade real-time response\n" . $herecurr); > > "in cases" is rather redundant. I did make this change. Thanx, Paul