On Wed, Dec 05, 2018 at 04:58:27PM -0800, Josh Triplett wrote: > On Thu, Dec 06, 2018 at 01:51:47AM +0100, Andrea Parri wrote: > > > commit 4f8f751961b536f77c8f82394963e8e2d26efd84 > > > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxx> > > > Date: Tue Dec 4 14:59:12 2018 -0800 > > > > > > torture: Explain and simplify odd "for" loop in mkinitrd.sh > > > > > > Why a Bourne-shell "for" loop? And why 192 instances of "a"? This commit > > > adds a shell comment to present the answer to these mysteries. It also > > > uses a series of factor-of-four Bourne-shell assignments to make it > > > easy to see how many instances there are, replacing the earlier wall of > > > 'a' characters. > > > > > > Reported-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx> > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx> > > > > > > diff --git a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh > > > index da298394daa2..ff69190604ea 100755 > > > --- a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh > > > +++ b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh > > > @@ -40,17 +40,24 @@ mkdir $T > > > cat > $T/init << '__EOF___' > > > #!/bin/sh > > > # Run in userspace a few milliseconds every second. This helps to > > > -# exercise the NO_HZ_FULL portions of RCU. > > > +# exercise the NO_HZ_FULL portions of RCU. The 192 instances of "a" was > > > +# empirically shown to give a nice multi-millisecond burst of user-mode > > > +# execution on a 2GHz CPU, as desired. Modern CPUs will vary from a > > > +# couple of milliseconds up to perhaps 100 milliseconds, which is an > > > +# acceptable range. > > > +# > > > +# Why not calibrate an exact delay? Because within this initrd, we > > > +# are restricted to Bourne-shell builtins, which as far as I know do not > > > +# provide any means of obtaining a fine-grained timestamp. > > > + > > > +a4="a a a a" > > > +a16="$a4 $a4 $a4 $a4" > > > +a64="$a8 $a8 $a8 $a8" > > > > Mmh, are you sure you don't want s/a8/a16/ here? ;-) > > ... *facepalm* Yeah, me as well... > Good catch. Thank you both!!! Thanx, Paul
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