From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
elver@google.com, dvyukov@google.com,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 03/12] rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs
Date: Wed, 12 Aug 2020 15:57:23 -0700 [thread overview]
Message-ID: <20200812225732.20068-3-paulmck@kernel.org> (raw)
In-Reply-To: <20200812225632.GA19759@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
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>
---
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 65e1b5e..d333f1b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -471,7 +471,7 @@ 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;
--
2.9.5
next prev parent reply other threads:[~2020-08-12 22:58 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 22:56 [PATCH tip/core/rcu 0/12] Add strict short-grace-period Kconfig option Paul E. McKenney
2020-08-12 22:57 ` [PATCH tip/core/rcu 01/12] rcu: Add Kconfig option for strict RCU grace periods paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 02/12] rcu: Reduce leaf fanout " paulmck
2020-08-12 22:57 ` paulmck [this message]
2020-08-12 22:57 ` [PATCH tip/core/rcu 04/12] rcu: Force DEFAULT_RCU_BLIMIT to 1000 for strict RCU GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 05/12] rcu: Always set .need_qs from __rcu_read_lock() for strict GPs paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 06/12] rcu: Do full report for .need_qs " paulmck
2020-08-13 0:50 ` Jann Horn
2020-08-13 3:29 ` Paul E. McKenney
2020-08-12 22:57 ` [PATCH tip/core/rcu 07/12] rcu: Attempt QS when CPU discovers GP " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 08/12] rcu: IPI all CPUs at GP start " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 09/12] rcu: IPI all CPUs at GP end " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 10/12] rcu: Provide optional RCU-reader exit delay " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 11/12] rcu: Execute RCU reader shortly after rcu_core " paulmck
2020-08-12 22:57 ` [PATCH tip/core/rcu 12/12] rcu: Report QS for outermost PREEMPT=n rcu_read_unlock() " paulmck
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