Messages in this thread | | | Date | Mon, 20 Jul 2015 17:41:04 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 15/16] scripts: Make checkpatch.pl warn on expedited RCU grace periods |
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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
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