linux-kernel - Re: [PATCH 1/2] rcu: provide rcu_virt_note_context

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Date:	Wed, 4 May 2011 09:35:42 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	linux-kernel@...r.kernel.org, avi@...hat.com, mtosatti@...hat.com,
	kvm@...r.kernel.org
Subject: Re: [PATCH 1/2] rcu: provide rcu_virt_note_context_switch()
 function.

On Wed, May 04, 2011 at 04:31:03PM +0300, Gleb Natapov wrote:
> Provide rcu_virt_note_context_switch() for vitalization use to note
> quiescent state during guest entry.

Very good, queued on -rcu.

Unless you tell me otherwise, I will assume that you want to carry the
patch modifying KVM to use this.

							Thanx, Paul

> Signed-off-by: Gleb Natapov <gleb@...hat.com>
> ---
>  include/linux/rcutiny.h |    8 ++++++++
>  include/linux/rcutree.h |   10 ++++++++++
>  kernel/rcutree.c        |    1 +
>  3 files changed, 19 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index 30ebd7c..52b3e02 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -100,6 +100,14 @@ static inline void rcu_note_context_switch(int cpu)
>  }
> 
>  /*
> + * Take advantage of the fact that there is only one CPU, which
> + * allows us to ignore virtualization-based context switches.
> + */
> +static inline void rcu_virt_note_context_switch(int cpu)
> +{
> +}
> +
> +/*
>   * Return the number of grace periods.
>   */
>  static inline long rcu_batches_completed(void)
> diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> index 3a93348..b2a906e 100644
> --- a/include/linux/rcutree.h
> +++ b/include/linux/rcutree.h
> @@ -35,6 +35,16 @@ extern void rcu_note_context_switch(int cpu);
>  extern int rcu_needs_cpu(int cpu);
>  extern void rcu_cpu_stall_reset(void);
> 
> +/*
> + * Note a virtualization-based context switch.  This is simply a
> + * wrapper around rcu_note_context_switch(), which allows TINY_RCU
> + * to save a few bytes.
> + */
> +static inline void rcu_virt_note_context_switch(int cpu)
> +{
> +	rcu_note_context_switch(cpu);
> +}
> +
>  #ifdef CONFIG_TREE_PREEMPT_RCU
> 
>  extern void exit_rcu(void);
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index dd4aea8..0837d63 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -124,6 +124,7 @@ void rcu_note_context_switch(int cpu)
>  	rcu_sched_qs(cpu);
>  	rcu_preempt_note_context_switch(cpu);
>  }
> +EXPORT_SYMBOL_GPL(rcu_note_context_switch);
> 
>  #ifdef CONFIG_NO_HZ
>  DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
> -- 
> 1.7.4.4
> 
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