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authorPaul E. McKenney <paulmck@kernel.org>2020-12-19 07:34:35 -0800
committerPaul E. McKenney <paulmck@kernel.org>2021-01-06 17:17:22 -0800
commit1afb95fee0342b8d9e05b0433e8e44a6dfd7c4a3 (patch)
tree914c500a93b70e478801a69c2018192dde0388f1 /kernel/torture.c
parent0b962c8fe0e5c72a252b236814a6b6e9df799061 (diff)
torture: Maintain torture-specific set of CPUs-online books
The TREE01 rcutorture scenario intentionally creates confusion as to the number of available CPUs by specifying the "maxcpus=8 nr_cpus=43" kernel boot parameters. This can disable rcutorture's load shedding, which currently uses num_online_cpus(), which would count the extra 35 CPUs. However, the rcutorture guest OS will be provisioned with only 8 CPUs, which means that rcutorture will present full load even when all but one of the original 8 CPUs are offline. This can result in spurious errors due to extreme overloading of that single remaining CPU. This commit therefore keeps a separate set of books on the number of usable online CPUs, so that torture_num_online_cpus() is used for load shedding instead of num_online_cpus(). Note that initial sizing must use num_online_cpus() because torture_num_online_cpus() will return NR_CPUS until shortly after torture_onoff_init() is invoked. Reported-by: Frederic Weisbecker <frederic@kernel.org> [ paulmck: Apply feedback from kernel test robot. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/torture.c')
-rw-r--r--kernel/torture.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/kernel/torture.c b/kernel/torture.c
index 507a20be6950..01e336f1e5b2 100644
--- a/kernel/torture.c
+++ b/kernel/torture.c
@@ -175,6 +175,19 @@ static unsigned long sum_online;
static int min_online = -1;
static int max_online;
+static int torture_online_cpus = NR_CPUS;
+
+/*
+ * Some torture testing leverages confusion as to the number of online
+ * CPUs. This function returns the torture-testing view of this number,
+ * which allows torture tests to load-balance appropriately.
+ */
+int torture_num_online_cpus(void)
+{
+ return READ_ONCE(torture_online_cpus);
+}
+EXPORT_SYMBOL_GPL(torture_num_online_cpus);
+
/*
* Attempt to take a CPU offline. Return false if the CPU is already
* offline or if it is not subject to CPU-hotplug operations. The
@@ -229,6 +242,8 @@ bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
*min_offl = delta;
if (*max_offl < delta)
*max_offl = delta;
+ WRITE_ONCE(torture_online_cpus, torture_online_cpus - 1);
+ WARN_ON_ONCE(torture_online_cpus <= 0);
}
return true;
@@ -285,6 +300,7 @@ bool torture_online(int cpu, long *n_onl_attempts, long *n_onl_successes,
*min_onl = delta;
if (*max_onl < delta)
*max_onl = delta;
+ WRITE_ONCE(torture_online_cpus, torture_online_cpus + 1);
}
return true;

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