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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-11-24 15:44:06 -0800
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-12-04 12:26:53 -0800
commit5a9be7c628c5273f84abacebf7faf2488376e0f0 (patch)
tree4d39aabecb8cc7542a053b3f9761f8e119f25450 /kernel/rcu/tree_plugin.h
parent72611ab9f5d2d384a04e72d560c9c82463115cbf (diff)
downloadlinux-sh-5a9be7c628c5273f84abacebf7faf2488376e0f0.tar.gz
rcu: Add rcu_normal kernel parameter to suppress expediting
Although expedited grace periods can be quite useful, and although their OS jitter has been greatly reduced, they can still pose problems for extreme real-time workloads. This commit therefore adds a rcu_normal kernel boot parameter (which can also be manipulated via sysfs) to suppress expedited grace periods, that is, to treat requests for expedited grace periods as if they were requests for normal grace periods. If both rcu_expedited and rcu_normal are specified, rcu_normal wins. This means that if you are relying on expedited grace periods to speed up boot, you will want to specify rcu_expedited on the kernel command line, and then specify rcu_normal via sysfs once boot completes. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/rcu/tree_plugin.h')
-rw-r--r--kernel/rcu/tree_plugin.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 57ba873d2f18..d45df3781551 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -746,6 +746,12 @@ void synchronize_rcu_expedited(void)
struct rcu_state *rsp = rcu_state_p;
unsigned long s;
+ /* If expedited grace periods are prohibited, fall back to normal. */
+ if (rcu_gp_is_normal()) {
+ wait_rcu_gp(call_rcu);
+ return;
+ }
+
s = rcu_exp_gp_seq_snap(rsp);
rnp_unlock = exp_funnel_lock(rsp, s);