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,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 06/13] rcu: Do full report for .need_qs for strict GPs
Date: Mon, 31 Aug 2020 11:11:13 -0700 [thread overview]
Message-ID: <20200831181120.1044-6-paulmck@kernel.org> (raw)
In-Reply-To: <20200831181101.GA950@paulmck-ThinkPad-P72>
From: "Paul E. McKenney" <paulmck@kernel.org>
The rcu_preempt_deferred_qs_irqrestore() function is invoked at
the end of an RCU read-side critical section (for example, directly
from rcu_read_unlock()) and, if .need_qs is set, invokes rcu_qs() to
report the new quiescent state. This works, except that rcu_qs() only
updates per-CPU state, leaving reporting of the actual quiescent state
to a later call to rcu_report_qs_rdp(), for example from within a later
RCU_SOFTIRQ instance. Although this approach is exactly what you want if
you are more concerned about efficiency than about short grace periods,
in CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, short grace periods are
the name of the game.
This commit therefore makes rcu_preempt_deferred_qs_irqrestore() directly
invoke rcu_report_qs_rdp() in CONFIG_RCU_STRICT_GRACE_PERIOD=y, thus
shortening grace periods.
Historical note: To the best of my knowledge, causing rcu_read_unlock()
to directly report a quiescent state first appeared in Jim Houston's
and Joe Korty's JRCU. This is the second instance of a Linux-kernel RCU
feature being inspired by JRCU, the first being RCU callback offloading
(as in the RCU_NOCB_CPU Kconfig option).
Reported-by Jann Horn <jannh@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
kernel/rcu/tree_plugin.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 668bbd2..dfdb902 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -459,8 +459,12 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
return;
}
t->rcu_read_unlock_special.s = 0;
- if (special.b.need_qs)
- rcu_qs();
+ if (special.b.need_qs) {
+ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
+ rcu_report_qs_rdp(rdp->cpu, rdp);
+ else
+ rcu_qs();
+ }
/*
* Respond to a request by an expedited grace period for a
--
2.9.5
next prev parent reply other threads:[~2020-08-31 18:12 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-31 18:11 [PATCH tip/core/rcu 0/13] Add strict grace periods for KASAN use for v5.10 Paul E. McKenney
2020-08-31 18:11 ` [PATCH tip/core/rcu 01/13] rcu: Add Kconfig option for strict RCU grace periods paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 02/13] rcu: Reduce leaf fanout " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 03/13] rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 04/13] rcu: Force DEFAULT_RCU_BLIMIT to 1000 " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 05/13] rcu: Always set .need_qs from __rcu_read_lock() for strict GPs paulmck
2020-09-04 4:05 ` Boqun Feng
2020-09-04 13:41 ` Paul E. McKenney
2020-09-07 0:11 ` Boqun Feng
2020-09-07 2:33 ` Paul E. McKenney
2020-08-31 18:11 ` paulmck [this message]
2020-08-31 18:11 ` [PATCH tip/core/rcu 07/13] rcu: Attempt QS when CPU discovers GP " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 08/13] rcu: IPI all CPUs at GP start " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 09/13] rcu: IPI all CPUs at GP end " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 10/13] rcu: Provide optional RCU-reader exit delay " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 11/13] rcu: Execute RCU reader shortly after rcu_core " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 12/13] rcu: Report QS for outermost PREEMPT=n rcu_read_unlock() " paulmck
2020-08-31 18:11 ` [PATCH tip/core/rcu 13/13] rcu: Remove unused "cpu" parameter from rcu_report_qs_rdp() paulmck
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