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| author |  Frederic Weisbecker <frederic@kernel.org>
| 2021-10-19 02:08:13 +0200 |
|---|---|---|
| committer |  Paul E. McKenney <paulmck@kernel.org>
| 2021-12-07 16:24:44 -0800 |
| commit | 78ad37a2c50dfdb9a60e42bb9ee1da86d1fe770c (patch) | |
| tree | 0e9b0384c5978aed7c902c9e6bbd55625723bb52 /kernel/rcu | |
| parent | rcu/nocb: Use appropriate rcu_nocb_lock_irqsave() (diff) | |
| download | linux-78ad37a2c50dfdb9a60e42bb9ee1da86d1fe770c.tar.gz linux-78ad37a2c50dfdb9a60e42bb9ee1da86d1fe770c.tar.bz2 linux-78ad37a2c50dfdb9a60e42bb9ee1da86d1fe770c.zip | |
rcu/nocb: Limit number of softirq callbacks only on softirq
The current condition to limit the number of callbacks executed in a
row checks the offloaded state of the rdp. Not only is it volatile
but it is also misleading: the rcu_core() may well be executing
callbacks concurrently with NOCB kthreads, and the offloaded state
would then be verified on both cases. As a result the limit would
spuriously not apply anymore on softirq while in the middle of
(de-)offloading process.
Fix and clarify the condition with those constraints in mind:
_ If callbacks are processed either by rcuc or NOCB kthread, the call
to cond_resched_tasks_rcu_qs() is enough to take care of the overload.
_ If instead callbacks are processed by softirqs:
* If need_resched(), exit the callbacks processing
* Otherwise if CPU is idle we can continue
* Otherwise exit because a softirq shouldn't interrupt a task for too
long nor deprive other pending softirq vectors of the CPU.
Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 20587d035d03..4f4d9ea6a9cb 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2525,9 +2525,8 @@ static void rcu_do_batch(struct rcu_data *rdp) /* * Stop only if limit reached and CPU has something to do. */ - if (count >= bl && !offloaded && - (need_resched() || - (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) + if (count >= bl && in_serving_softirq() && + (need_resched() || !is_idle_task(current))) break; if (unlikely(tlimit)) { /* only call local_clock() every 32 callbacks */ |