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Message-ID: <20200827011826.GA1942571@google.com>
Date: Wed, 26 Aug 2020 21:18:26 -0400
From: Joel Fernandes <joel@...lfernandes.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, will@...nel.org,
npiggin@...il.com, elver@...gle.com, jgross@...e.com,
paulmck@...nel.org, rostedt@...dmis.org, rjw@...ysocki.net,
svens@...ux.ibm.com, tglx@...utronix.de
Subject: Re: [PATCH v2 03/11] sched,idle,rcu: Push rcu_idle deeper into the
idle path
On Fri, Aug 21, 2020 at 10:47:41AM +0200, Peter Zijlstra wrote:
> Lots of things take locks, due to a wee bug, rcu_lockdep didn't notice
> that the locking tracepoints were using RCU.
>
> Push rcu_idle_{enter,exit}() as deep as possible into the idle paths,
> this also resolves a lot of _rcuidle()/RCU_NONIDLE() usage.
>
> Specifically, sched_clock_idle_wakeup_event() will use ktime which
> will use seqlocks which will tickle lockdep, and
> stop_critical_timings() uses lock.
I was wondering if those tracepoints should just use _rcuidle variant of the
trace call. But that's a terrible idea considering that would add unwanted
overhead I think.
Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
thanks,
- Joel
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> Tested-by: Marco Elver <elver@...gle.com>
> ---
> drivers/cpuidle/cpuidle.c | 12 ++++++++----
> kernel/sched/idle.c | 22 ++++++++--------------
> 2 files changed, 16 insertions(+), 18 deletions(-)
>
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -145,13 +145,14 @@ static void enter_s2idle_proper(struct c
> * executing it contains RCU usage regarded as invalid in the idle
> * context, so tell RCU about that.
> */
> - RCU_NONIDLE(tick_freeze());
> + tick_freeze();
> /*
> * The state used here cannot be a "coupled" one, because the "coupled"
> * cpuidle mechanism enables interrupts and doing that with timekeeping
> * suspended is generally unsafe.
> */
> stop_critical_timings();
> + rcu_idle_enter();
> drv->states[index].enter_s2idle(dev, drv, index);
> if (WARN_ON_ONCE(!irqs_disabled()))
> local_irq_disable();
> @@ -160,7 +161,8 @@ static void enter_s2idle_proper(struct c
> * first CPU executing it calls functions containing RCU read-side
> * critical sections, so tell RCU about that.
> */
> - RCU_NONIDLE(tick_unfreeze());
> + rcu_idle_exit();
> + tick_unfreeze();
> start_critical_timings();
>
> time_end = ns_to_ktime(local_clock());
> @@ -229,16 +231,18 @@ int cpuidle_enter_state(struct cpuidle_d
> /* Take note of the planned idle state. */
> sched_idle_set_state(target_state);
>
> - trace_cpu_idle_rcuidle(index, dev->cpu);
> + trace_cpu_idle(index, dev->cpu);
> time_start = ns_to_ktime(local_clock());
>
> stop_critical_timings();
> + rcu_idle_enter();
> entered_state = target_state->enter(dev, drv, index);
> + rcu_idle_exit();
> start_critical_timings();
>
> sched_clock_idle_wakeup_event();
> time_end = ns_to_ktime(local_clock());
> - trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
> + trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu);
>
> /* The cpu is no longer idle or about to enter idle. */
> sched_idle_set_state(NULL);
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -54,17 +54,18 @@ __setup("hlt", cpu_idle_nopoll_setup);
>
> static noinline int __cpuidle cpu_idle_poll(void)
> {
> + trace_cpu_idle(0, smp_processor_id());
> + stop_critical_timings();
> rcu_idle_enter();
> - trace_cpu_idle_rcuidle(0, smp_processor_id());
> local_irq_enable();
> - stop_critical_timings();
>
> while (!tif_need_resched() &&
> - (cpu_idle_force_poll || tick_check_broadcast_expired()))
> + (cpu_idle_force_poll || tick_check_broadcast_expired()))
> cpu_relax();
> - start_critical_timings();
> - trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
> +
> rcu_idle_exit();
> + start_critical_timings();
> + trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id());
>
> return 1;
> }
> @@ -91,7 +92,9 @@ void __cpuidle default_idle_call(void)
> local_irq_enable();
> } else {
> stop_critical_timings();
> + rcu_idle_enter();
> arch_cpu_idle();
> + rcu_idle_exit();
> start_critical_timings();
> }
> }
> @@ -158,7 +161,6 @@ static void cpuidle_idle_call(void)
>
> if (cpuidle_not_available(drv, dev)) {
> tick_nohz_idle_stop_tick();
> - rcu_idle_enter();
>
> default_idle_call();
> goto exit_idle;
> @@ -178,21 +180,17 @@ static void cpuidle_idle_call(void)
> u64 max_latency_ns;
>
> if (idle_should_enter_s2idle()) {
> - rcu_idle_enter();
>
> entered_state = call_cpuidle_s2idle(drv, dev);
> if (entered_state > 0)
> goto exit_idle;
>
> - rcu_idle_exit();
> -
> max_latency_ns = U64_MAX;
> } else {
> max_latency_ns = dev->forced_idle_latency_limit_ns;
> }
>
> tick_nohz_idle_stop_tick();
> - rcu_idle_enter();
>
> next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
> call_cpuidle(drv, dev, next_state);
> @@ -209,8 +207,6 @@ static void cpuidle_idle_call(void)
> else
> tick_nohz_idle_retain_tick();
>
> - rcu_idle_enter();
> -
> entered_state = call_cpuidle(drv, dev, next_state);
> /*
> * Give the governor an opportunity to reflect on the outcome
> @@ -226,8 +222,6 @@ static void cpuidle_idle_call(void)
> */
> if (WARN_ON_ONCE(irqs_disabled()))
> local_irq_enable();
> -
> - rcu_idle_exit();
> }
>
> /*
>
>
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