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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
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')
-rw-r--r--kernel/rcu/srcu.c2
-rw-r--r--kernel/rcu/tree.c6
-rw-r--r--kernel/rcu/tree_plugin.h6
-rw-r--r--kernel/rcu/update.c12
4 files changed, 25 insertions, 1 deletions
diff --git a/kernel/rcu/srcu.c b/kernel/rcu/srcu.c
index a63a1ea5a41b..9b9cdd549caa 100644
--- a/kernel/rcu/srcu.c
+++ b/kernel/rcu/srcu.c
@@ -489,7 +489,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
*/
void synchronize_srcu(struct srcu_struct *sp)
{
- __synchronize_srcu(sp, rcu_gp_is_expedited()
+ __synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal())
? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
: SYNCHRONIZE_SRCU_TRYCOUNT);
}
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6a652d1f3d7f..489992997c06 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3841,6 +3841,12 @@ void synchronize_sched_expedited(void)
if (rcu_blocking_is_gp())
return;
+ /* If expedited grace periods are prohibited, fall back to normal. */
+ if (rcu_gp_is_normal()) {
+ wait_rcu_gp(call_rcu_sched);
+ return;
+ }
+
/* Take a snapshot of the sequence number. */
s = rcu_exp_gp_seq_snap(rsp);
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);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 5f748c5a40f0..8fccda3a794d 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -61,6 +61,7 @@ MODULE_ALIAS("rcupdate");
#define MODULE_PARAM_PREFIX "rcupdate."
module_param(rcu_expedited, int, 0);
+module_param(rcu_normal, int, 0);
#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT)
/**
@@ -113,6 +114,17 @@ EXPORT_SYMBOL(rcu_read_lock_sched_held);
#ifndef CONFIG_TINY_RCU
+/*
+ * Should expedited grace-period primitives always fall back to their
+ * non-expedited counterparts? Intended for use within RCU. Note
+ * that if the user specifies both rcu_expedited and rcu_normal, then
+ * rcu_normal wins.
+ */
+bool rcu_gp_is_normal(void)
+{
+ return READ_ONCE(rcu_normal);
+}
+
static atomic_t rcu_expedited_nesting =
ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0);