rcutorture: Allow negative values of nreaders to oversubscribe (3838cc18) · Commits · 戴 / test

By default, with rcutorture.nreaders equal to -1, rcutorture provisions N-1 reader kthreads, where N is the number of CPUs. This avoids rcutorture-induced stalls, but also avoids heavier levels of torture. This commit therefore allows negative values of rcutorture.nreaders to specify larger numbers of reader kthreads, so that for example rcutorture.nreaders=-2 provisions N kthreads and rcutorture.nreaders=-5 provisions N+3 kthreads. Signed-off-by:

Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Update documentation, as suggested by Josh Triplett. ]

Documentation/kernel-parameters.txt

+5 −1

Original line number	Diff line number	Diff line
		@@ -3101,7 +3101,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
		test, hence the "fake".

		rcutorture.nreaders= [KNL]
		Set number of RCU readers.
		Set number of RCU readers. The value -1 selects
		N-1, where N is the number of CPUs. A value
		"n" less than -1 selects N-n-2, where N is again
		the number of CPUs. For example, -2 selects N
		(the number of CPUs), -3 selects N+1, and so on.

		rcutorture.object_debug= [KNL]
		Enable debug-object double-call_rcu() testing.

kernel/rcu/rcutorture.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1701,7 +1701,7 @@ rcu_torture_init(void)
		if (nreaders >= 0) {
		nrealreaders = nreaders;
		} else {
		nrealreaders = num_online_cpus() - 1;
		nrealreaders = num_online_cpus() - 2 - nreaders;
		if (nrealreaders <= 0)
		nrealreaders = 1;
		}

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