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authorPaul E. McKenney <paulmck@kernel.org>2020-08-05 17:25:23 -0700
committerPaul E. McKenney <paulmck@kernel.org>2020-08-24 18:40:24 -0700
commitaecd34b9765de3b58c98a1d75b982fc64becd1e9 (patch)
treee24b28222c483c0fdcb19a4ef2d6e4cc291b5d9a /kernel
parentdc1269186bed3afc5a2018527516be84fe55d3e0 (diff)
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rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs
If there are idle CPUs, RCU's grace-period kthread will wait several jiffies before even thinking about polling them. This promotes efficiency, which is normally a good thing, but when the kernel has been built with CONFIG_RCU_STRICT_GRACE_PERIOD=y, we care more about short grace periods. This commit therefore restricts the default jiffies_till_first_fqs value to zero in kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y, which causes RCU's grace-period kthread to poll for idle CPUs immediately after starting a grace period. Reported-by Jann Horn <jannh@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/tree.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 8ce77d9ac716..85511590fc38 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -485,7 +485,7 @@ module_param(qhimark, long, 0444);
module_param(qlowmark, long, 0444);
module_param(qovld, long, 0444);
-static ulong jiffies_till_first_fqs = ULONG_MAX;
+static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
static ulong jiffies_till_next_fqs = ULONG_MAX;
static bool rcu_kick_kthreads;
static int rcu_divisor = 7;