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rcutorture: Allow negative values of nreaders to oversubscribe

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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. ]
This commit is contained in:
Paul E. McKenney 2015-03-12 13:55:48 -07:00
parent 6530b3f4c5
commit 3838cc1850
2 changed files with 6 additions and 2 deletions
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6
Documentation/kernel-parameters.txt
View file

@ -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.

2
kernel/rcu/rcutorture.c
View file

@ -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;
}