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McKenney" To: Andrea Parri Cc: Josh Triplett , tglx@linutronix.de, mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org Subject: Re: [tip:core/rcu] rcutorture: Make initrd/init execute in userspace Reply-To: paulmck@linux.ibm.com References: <20181204222412.GA6874@localhost> <20181204230423.GP4170@linux.ibm.com> <20181205222523.GA14609@localhost> <20181206000809.GX4170@linux.ibm.com> <20181206005147.GA3300@andrea> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181206005147.GA3300@andrea> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18120601-0064-0000-0000-0000038169E5 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010178; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000270; SDB=6.01127571; UDB=6.00585688; IPR=6.00907705; MB=3.00024466; MTD=3.00000008; XFM=3.00000015; UTC=2018-12-06 01:05:40 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18120601-0065-0000-0000-00003B93D20C Message-Id: <20181206010537.GZ4170@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-12-05_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1812060006 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 06, 2018 at 01:51:47AM +0100, Andrea Parri wrote: > > commit 4f8f751961b536f77c8f82394963e8e2d26efd84 > > Author: Paul E. McKenney > > 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 > > Signed-off-by: Paul E. McKenney > > > > 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? ;-) Indeed I do! How about the following? Thanx, Paul ------------------------------------------------------------------------ commit 94cae122408cdc55470360868a1a4b8f160e576d Author: Paul E. McKenney 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 Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett [ paulmck: Fix wrong-variable bugs noted by Andrea Parri. ] diff --git a/tools/testing/selftests/rcutorture/bin/mkinitrd.sh b/tools/testing/selftests/rcutorture/bin/mkinitrd.sh index da298394daa2..e79eb35c41e2 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 $a4" +a64="$a16 $a16 $a16 $a16" +a192="$a64 $a64 $a64" while : do q= - for i in \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a \ - a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a + for i in $a192 do q="$q $i" done