The following commit has been merged into the core/rcu branch of tip: Commit-ID: aecd34b9765de3b58c98a1d75b982fc64becd1e9 Gitweb: https://git.kernel.org/tip/aecd34b9765de3b58c98a1d75b982fc64becd1e9 Author: Paul E. McKenney <paulmck@xxxxxxxxxx> AuthorDate: Wed, 05 Aug 2020 17:25:23 -07:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Mon, 24 Aug 2020 18:40:24 -07:00 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@xxxxxxxxxx> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8ce77d9..8551159 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;
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