linux-kernel - [PATCH tip/core/rcu 5/5] torture: Make jitter.sh handle large systems

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Date:   Wed,  3 Mar 2021 16:29:55 -0800
From:   paulmck@...nel.org
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.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, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH tip/core/rcu 5/5] torture: Make jitter.sh handle large systems

From: "Paul E. McKenney" <paulmck@...nel.org>

The current jitter.sh script expects cpumask bits to fit into whatever
the awk interpreter uses for an integer, which clearly does not hold for
even medium-sized systems these days.  This means that on a large system,
only the first 32 or 64 CPUs (depending) are subjected to jitter.sh
CPU-time perturbations.  This commit therefore computes a given CPU's
cpumask using text manipulation rather than arithmetic shifts.

Reported-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 tools/testing/selftests/rcutorture/bin/jitter.sh | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/rcutorture/bin/jitter.sh b/tools/testing/selftests/rcutorture/bin/jitter.sh
index 188b864..3a856ec 100755
--- a/tools/testing/selftests/rcutorture/bin/jitter.sh
+++ b/tools/testing/selftests/rcutorture/bin/jitter.sh
@@ -67,10 +67,10 @@ do
 		srand(n + me + systime());
 		ncpus = split(cpus, ca);
 		curcpu = ca[int(rand() * ncpus + 1)];
-		mask = lshift(1, curcpu);
-		if (mask + 0 <= 0)
-			mask = 1;
-		printf("%#x\n", mask);
+		z = "";
+		for (i = 1; 4 * i <= curcpu; i++)
+			z = z "0";
+		print "0x" 2 ^ (curcpu % 4) z;
 	}' < /dev/null`
 	n=$(($n+1))
 	if ! taskset -p $cpumask $$ > /dev/null 2>&1
-- 
2.9.5