From: "Paul E. McKenney" <paulmck@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de, frederic@kernel.org,
linux-kernel@vger.kernel.org, x86@kernel.org, cai@lca.pw,
mgorman@techsingularity.net, joel@joelfernandes.org
Subject: Re: [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi()
Date: Wed, 27 May 2020 12:39:14 -0700 [thread overview]
Message-ID: <20200527193914.GW2869@paulmck-ThinkPad-P72> (raw)
In-Reply-To: <20200527171236.GC706495@hirez.programming.kicks-ass.net>
On Wed, May 27, 2020 at 07:12:36PM +0200, Peter Zijlstra wrote:
> On Wed, May 27, 2020 at 06:35:43PM +0200, Peter Zijlstra wrote:
> > Right, I went though them, didn't find anything obvious amiss. OK, let
> > me do a nicer patch.
>
> something like so then?
>
> ---
> Subject: rcu: Allow for smp_call_function() running callbacks from idle
>
> Current RCU hard relies on smp_call_function() callbacks running from
> interrupt context. A pending optimization is going to break that, it
> will allow idle CPUs to run the callbacks from the idle loop. This
> avoids raising the IPI on the requesting CPU and avoids handling an
> exception on the receiving CPU.
>
> Change rcu_is_cpu_rrupt_from_idle() to also accept task context,
> provided it is the idle task.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Looks good to me!
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
> ---
> kernel/rcu/tree.c | 25 +++++++++++++++++++------
> kernel/sched/idle.c | 4 ++++
> 2 files changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index d8e9dbbefcfa..c716eadc7617 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -418,16 +418,23 @@ void rcu_momentary_dyntick_idle(void)
> EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
>
> /**
> - * rcu_is_cpu_rrupt_from_idle - see if interrupted from idle
> + * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
> *
> * If the current CPU is idle and running at a first-level (not nested)
> - * interrupt from idle, return true. The caller must have at least
> - * disabled preemption.
> + * interrupt, or directly, from idle, return true.
> + *
> + * The caller must have at least disabled IRQs.
> */
> static int rcu_is_cpu_rrupt_from_idle(void)
> {
> - /* Called only from within the scheduling-clock interrupt */
> - lockdep_assert_in_irq();
> + long nesting;
> +
> + /*
> + * Usually called from the tick; but also used from smp_function_call()
> + * for expedited grace periods. This latter can result in running from
> + * the idle task, instead of an actual IPI.
> + */
> + lockdep_assert_irqs_disabled();
>
> /* Check for counter underflows */
> RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0,
> @@ -436,9 +443,15 @@ static int rcu_is_cpu_rrupt_from_idle(void)
> "RCU dynticks_nmi_nesting counter underflow/zero!");
>
> /* Are we at first interrupt nesting level? */
> - if (__this_cpu_read(rcu_data.dynticks_nmi_nesting) != 1)
> + nesting = __this_cpu_read(rcu_data.dynticks_nmi_nesting);
> + if (nesting > 1)
> return false;
>
> + /*
> + * If we're not in an interrupt, we must be in the idle task!
> + */
> + WARN_ON_ONCE(!nesting && !is_idle_task(current));
> +
> /* Does CPU appear to be idle from an RCU standpoint? */
> return __this_cpu_read(rcu_data.dynticks_nesting) == 0;
> }
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index e9cef84c2b70..05deb81bb3e3 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -289,6 +289,10 @@ static void do_idle(void)
> */
> smp_mb__after_atomic();
>
> + /*
> + * RCU relies on this call to be done outside of an RCU read-side
> + * critical section.
> + */
> flush_smp_call_function_from_idle();
> schedule_idle();
>
next prev parent reply other threads:[~2020-05-27 19:39 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-26 16:10 [RFC][PATCH 0/7] Fix the scheduler-IPI mess Peter Zijlstra
2020-05-26 16:10 ` [RFC][PATCH 1/7] sched: Fix smp_call_function_single_async() usage for ILB Peter Zijlstra
2020-05-26 23:56 ` Frederic Weisbecker
2020-05-27 10:23 ` Vincent Guittot
2020-05-27 11:28 ` Frederic Weisbecker
2020-05-27 12:07 ` Vincent Guittot
2020-05-29 15:26 ` Valentin Schneider
2020-06-01 9:52 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-06-01 11:40 ` Frederic Weisbecker
2020-05-26 16:10 ` [RFC][PATCH 2/7] smp: Optimize flush_smp_call_function_queue() Peter Zijlstra
2020-05-28 12:28 ` Frederic Weisbecker
2020-06-01 9:52 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 3/7] smp: Move irq_work_run() out of flush_smp_call_function_queue() Peter Zijlstra
2020-05-29 13:04 ` Frederic Weisbecker
2020-06-01 9:52 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi() Peter Zijlstra
2020-05-27 9:56 ` Peter Zijlstra
2020-05-27 10:15 ` Peter Zijlstra
2020-05-27 15:56 ` Paul E. McKenney
2020-05-27 16:35 ` Peter Zijlstra
2020-05-27 17:12 ` Peter Zijlstra
2020-05-27 19:39 ` Paul E. McKenney [this message]
2020-05-28 1:35 ` Joel Fernandes
2020-05-28 8:59 ` [tip: core/rcu] rcu: Allow for smp_call_function() running callbacks from idle tip-bot2 for Peter Zijlstra
2021-01-21 16:56 ` [RFC][PATCH 4/7] smp: Optimize send_call_function_single_ipi() Peter Zijlstra
2021-01-22 0:20 ` Paul E. McKenney
2021-01-22 8:31 ` Peter Zijlstra
2021-01-22 15:35 ` Paul E. McKenney
2020-05-29 13:01 ` Frederic Weisbecker
2020-06-01 9:52 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 5/7] irq_work, smp: Allow irq_work on call_single_queue Peter Zijlstra
2020-05-28 23:40 ` Frederic Weisbecker
2020-05-29 13:36 ` Peter Zijlstra
2020-06-05 9:37 ` Peter Zijlstra
2020-06-05 15:02 ` Frederic Weisbecker
2020-06-05 16:17 ` Peter Zijlstra
2020-06-05 15:24 ` Kees Cook
2020-06-10 13:24 ` Frederic Weisbecker
2020-06-01 9:52 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 6/7] sched: Add rq::ttwu_pending Peter Zijlstra
2020-06-01 9:52 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-05-26 16:11 ` [RFC][PATCH 7/7] sched: Replace rq::wake_list Peter Zijlstra
2020-05-29 15:10 ` Valdis Klētnieks
2020-06-01 9:52 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2020-06-02 15:16 ` Frederic Weisbecker
2020-06-04 14:18 ` [RFC][PATCH 7/7] " Guenter Roeck
2020-06-05 0:24 ` Eric Biggers
2020-06-05 7:41 ` Peter Zijlstra
2020-06-05 16:15 ` Eric Biggers
2020-06-06 23:13 ` Guenter Roeck
2020-06-09 20:21 ` Eric Biggers
2020-06-09 21:25 ` Guenter Roeck
2020-06-09 21:38 ` Eric Biggers
2020-06-09 22:06 ` Peter Zijlstra
2020-06-09 23:03 ` Guenter Roeck
2020-06-10 9:09 ` Peter Zijlstra
2020-06-18 17:57 ` Steven Rostedt
2020-06-18 19:06 ` Guenter Roeck
2020-06-09 22:07 ` Peter Zijlstra
2020-06-05 8:10 ` Peter Zijlstra
2020-06-05 13:33 ` Guenter Roeck
2020-06-05 14:09 ` Peter Zijlstra
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