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Message-ID: <20230112012950.GE4028633@paulmck-ThinkPad-P17-Gen-1>
Date: Wed, 11 Jan 2023 17:29:50 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc: linux-kernel@...r.kernel.org,
Josh Triplett <josh@...htriplett.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
rcu@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
fweisbec@...il.com, urezki@...il.com
Subject: Re: [PATCH v2 rcu/dev 1/2] rcu: Track laziness during boot and
suspend
On Thu, Jan 12, 2023 at 12:52:22AM +0000, Joel Fernandes (Google) wrote:
> During boot and suspend/resume, it is desired to prevent RCU laziness from
> effecting performance and in some cases failures like with suspend.
>
> Track whether RCU laziness is to be ignored or not, in kernels with
> CONFIG_RCU_LAZY enabled. We do such tracking for expedited-RCU already, however
> since Android currently expedites synchronous_rcu() always, we cannot rely on
> that. The next patch ignores laziness hints based on this tracking.
>
> Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> ---
> Paul, could we take this and the next one for 6.2 -rc cycle?
Given how late it is in v6.2, I would need you to make it all depend on
CONFIG_RCU_LAZY, so that it is blindingly and immediately obvious that
there is no change in behavior for kernels built with CONFIG_RCU_LAZY=n.
If you are OK with the v6.3 merge window and backports, what you have
likely suffices, modulo review and testing.
So, how would you like to proceed?
Thanx, Paul
> I also booted debian Linux and verified the flag is reset correctly after boot
> completes. Thanks.
>
> kernel/rcu/rcu.h | 6 ++++++
> kernel/rcu/tree.c | 2 ++
> kernel/rcu/update.c | 40 +++++++++++++++++++++++++++++++++++++++-
> 5 files changed, 55 insertions(+), 1 deletion(-)
> create mode 100644 cc_list
> create mode 100644 to_list
>
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index 5c8013f7085f..115616ac3bfa 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -449,14 +449,20 @@ do { \
> /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
> static inline bool rcu_gp_is_normal(void) { return true; }
> static inline bool rcu_gp_is_expedited(void) { return false; }
> +static inline bool rcu_async_should_hurry(void) { return false; }
> static inline void rcu_expedite_gp(void) { }
> static inline void rcu_unexpedite_gp(void) { }
> +static inline void rcu_async_hurry(void) { }
> +static inline void rcu_async_relax(void) { }
> static inline void rcu_request_urgent_qs_task(struct task_struct *t) { }
> #else /* #ifdef CONFIG_TINY_RCU */
> bool rcu_gp_is_normal(void); /* Internal RCU use. */
> bool rcu_gp_is_expedited(void); /* Internal RCU use. */
> +bool rcu_async_should_hurry(void); /* Internal RCU use. */
> void rcu_expedite_gp(void);
> void rcu_unexpedite_gp(void);
> +void rcu_async_hurry(void);
> +void rcu_async_relax(void);
> void rcupdate_announce_bootup_oddness(void);
> #ifdef CONFIG_TASKS_RCU_GENERIC
> void show_rcu_tasks_gp_kthreads(void);
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 63545d79da51..78b2e999c904 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4504,11 +4504,13 @@ static int rcu_pm_notify(struct notifier_block *self,
> switch (action) {
> case PM_HIBERNATION_PREPARE:
> case PM_SUSPEND_PREPARE:
> + rcu_async_hurry();
> rcu_expedite_gp();
> break;
> case PM_POST_HIBERNATION:
> case PM_POST_SUSPEND:
> rcu_unexpedite_gp();
> + rcu_async_relax();
> break;
> default:
> break;
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index 3893022f8ed8..19bf6fa3ee6a 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -144,8 +144,45 @@ bool rcu_gp_is_normal(void)
> }
> EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
>
> -static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
> +static atomic_t rcu_async_hurry_nesting = ATOMIC_INIT(1);
> +/*
> + * Should call_rcu() callbacks be processed with urgency or are
> + * they OK being executed with arbitrary delays?
> + */
> +bool rcu_async_should_hurry(void)
> +{
> + return !IS_ENABLED(CONFIG_RCU_LAZY) ||
> + atomic_read(&rcu_async_hurry_nesting);
> +}
> +EXPORT_SYMBOL_GPL(rcu_async_should_hurry);
> +
> +/**
> + * rcu_async_hurry - Make future async RCU callbacks not lazy.
> + *
> + * After a call to this function, future calls to call_rcu()
> + * will be processed in a timely fashion.
> + */
> +void rcu_async_hurry(void)
> +{
> + if (IS_ENABLED(CONFIG_RCU_LAZY))
> + atomic_inc(&rcu_async_hurry_nesting);
> +}
> +EXPORT_SYMBOL_GPL(rcu_async_hurry);
>
> +/**
> + * rcu_async_relax - Make future async RCU callbacks lazy.
> + *
> + * After a call to this function, future calls to call_rcu()
> + * will be processed in a lazy fashion.
> + */
> +void rcu_async_relax(void)
> +{
> + if (IS_ENABLED(CONFIG_RCU_LAZY))
> + atomic_dec(&rcu_async_hurry_nesting);
> +}
> +EXPORT_SYMBOL_GPL(rcu_async_relax);
> +
> +static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
> /*
> * Should normal grace-period primitives be expedited? Intended for
> * use within RCU. Note that this function takes the rcu_expedited
> @@ -195,6 +232,7 @@ static bool rcu_boot_ended __read_mostly;
> void rcu_end_inkernel_boot(void)
> {
> rcu_unexpedite_gp();
> + rcu_async_relax();
> if (rcu_normal_after_boot)
> WRITE_ONCE(rcu_normal, 1);
> rcu_boot_ended = true;
> --
> 2.39.0.314.g84b9a713c41-goog
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