From 3838cc1850ccd09f93e729e9047ec1995026f83e Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 12 Mar 2015 13:55:48 -0700 Subject: [PATCH] rcutorture: Allow negative values of nreaders to oversubscribe 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: Update documentation, as suggested by Josh Triplett. ] --- Documentation/kernel-parameters.txt | 6 +++++- kernel/rcu/rcutorture.c | 2 +- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 61ab1628a057..04b811086dca 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -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. diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index a67ef6ff86b0..7294d605c481 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -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; } -- GitLab