The TREE01.boot nr_cpus kernel boot parameter has been set to 43 for more than seven years, but it can cause RCU CPU stall warnings on arm64, most of the time involving the stop-machine subsystem. This should not be too surprising, given that this causes 43 vCPUs to spin with interrupts disabled when there are only eight physical CPUs.
The point of this CPU overcommit is to test the ability of expedited RCU grace period initialization to handle races with incoming CPUs that have never previously been online. But limiting to 17 CPUs instead of 43 allows time for this code to be exercised, and eliminates (or at least greatly reduces) the incidence of RCU CPU stall warnings on arm64. So this commit therefore sets nr_cpus=17 in TREE01.boot. Signed-off-by: Paul E. McKenney <paul...@kernel.org> --- tools/testing/selftests/rcutorture/configs/rcu/TREE01.boot | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE01.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE01.boot index 40af3df0f397f..1cc5b47dde282 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE01.boot +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE01.boot @@ -1,4 +1,4 @@ -maxcpus=8 nr_cpus=43 +maxcpus=8 nr_cpus=17 rcutree.gp_preinit_delay=3 rcutree.gp_init_delay=3 rcutree.gp_cleanup_delay=3 -- 2.40.1
