Re: [PATCH tip/core/rcu 07/26] rcu: Switch task's syscall hooks on context switch

Josh Triplett
2012-08-31T23:48:47Z

On Thu, Aug 30, 2012 at 02:05:24PM -0700, Paul E. McKenney wrote:
> From: Frederic Weisbecker <fweisbec@gmail.com>
>
> Clear the syscalls hook of a task when it's scheduled out so that if
> the task migrates, it doesn't run the syscall slow path on a CPU
> that might not need it.
>
> Also set the syscalls hook on the next task if needed.
>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Alessio Igor Bogani <abogani@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Chris Metcalf <cmetcalf@tilera.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Geoff Levand <geoff@infradead.org>
> Cc: Gilad Ben Yossef <gilad@benyossef.com>
> Cc: Hakan Akkan <hakanakkan@gmail.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Kevin Hilman <khilman@ti.com>
> Cc: Max Krasnyansky <maxk@qualcomm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Stephen Hemminger <shemminger@vyatta.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

> arch/um/drivers/mconsole_kern.c | 1 +
> include/linux/rcupdate.h | 2 ++
> include/linux/sched.h | 8 ++++++++
> kernel/rcutree.c | 15 +++++++++++++++
> kernel/sched/core.c | 1 +
> 5 files changed, 27 insertions(+), 0 deletions(-)
>
> diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_kern.c
> index 664a60e..c17de0d 100644
> --- a/arch/um/drivers/mconsole_kern.c
> +++ b/arch/um/drivers/mconsole_kern.c
> @@ -705,6 +705,7 @@ static void stack_proc(void *arg)
> struct task_struct *from = current, *to = arg;
>
> to->thread.saved_task = from;
> + rcu_switch(from, to);
> switch_to(from, to, from);
> }
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index e411117..1fc0a0e 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -197,6 +197,8 @@ extern void rcu_user_enter(void);
> extern void rcu_user_exit(void);
> extern void rcu_user_enter_irq(void);
> extern void rcu_user_exit_irq(void);
> +extern void rcu_user_hooks_switch(struct task_struct *prev,
> + struct task_struct *next);
> #else
> static inline void rcu_user_enter(void) { }
> static inline void rcu_user_exit(void) { }
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index c147e70..e4d5936 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1894,6 +1894,14 @@ static inline void rcu_copy_process(struct task_struct *p)
>
> #endif
>
> +static inline void rcu_switch(struct task_struct *prev,
> + struct task_struct *next)
> +{
> +#ifdef CONFIG_RCU_USER_QS
> + rcu_user_hooks_switch(prev, next);
> +#endif
> +}
> +
> static inline void tsk_restore_flags(struct task_struct *task,
> unsigned long orig_flags, unsigned long flags)
> {
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index e2fd370..af92681 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -721,6 +721,21 @@ int rcu_is_cpu_idle(void)
> }
> EXPORT_SYMBOL(rcu_is_cpu_idle);
>
> +#ifdef CONFIG_RCU_USER_QS
> +void rcu_user_hooks_switch(struct task_struct *prev,
> + struct task_struct *next)
> +{
> + struct rcu_dynticks *rdtp;
> +
> + /* Interrupts are disabled in context switch */
> + rdtp = &__get_cpu_var(rcu_dynticks);
> + if (!rdtp->ignore_user_qs) {
> + clear_tsk_thread_flag(prev, TIF_NOHZ);
> + set_tsk_thread_flag(next, TIF_NOHZ);
> + }
> +}
> +#endif /* #ifdef CONFIG_RCU_USER_QS */
> +
> #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
>
> /*
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index d325c4b..07c6d9a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2081,6 +2081,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
> #endif
>
> /* Here we just switch the register state and the stack. */
> + rcu_switch(prev, next);
> switch_to(prev, next, prev);
>
> barrier();
> --
> 1.7.8
>