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Date: Mon, 20 Jul 2015 17:41:04 -0700 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Joe Perches <joe@...ches.com> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com, Andy Whitcroft <apw@...onical.com> Subject: Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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