Re: [PATCH tip/core/rcu 13/14] rcu: Split RCU core processing out of __call_rcu()

[Josh Triplett <josh@joshtriplett.org>]

On Fri, Jun 15, 2012 at 01:13:14PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> The __call_rcu() function is a bit overweight, so this commit splits
> it into actual enqueuing of and accounting for the callback (__call_rcu())
> and associated RCU-core processing (__call_rcu_core()).
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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

>  kernel/rcutree.c |   55 ++++++++++++++++++++++++++++++++++++++++++++++++-----
>  1 files changed, 49 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 9419ebf..6940a81 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -1858,9 +1858,11 @@ static void invoke_rcu_core(void)
>  	raise_softirq(RCU_SOFTIRQ);
>  }
>  
> -static void
> -__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
> -	   struct rcu_state *rsp, bool lazy)
> +/*
> + * Handle any core-RCU processing required by a call_rcu() invocation.
> + */
> +static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
> +			    struct rcu_head *head, unsigned long flags)
>  {
>  	unsigned long flags;
>  	struct rcu_data *rdp;
> @@ -1905,10 +1907,8 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
>  		invoke_rcu_core();
>  
>  	/* If interrupts were disabled or CPU offline, don't invoke RCU core. */
> -	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) {
> -		local_irq_restore(flags);
> +	if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
>  		return;
> -	}
>  
>  	/*
>  	 * Force the grace period if too many callbacks or too long waiting.
> @@ -1941,6 +1941,49 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
>  		}
>  	} else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
>  		force_quiescent_state(rsp, 1);
> +}
> +
> +static void
> +__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
> +	   struct rcu_state *rsp, bool lazy)
> +{
> +	unsigned long flags;
> +	struct rcu_data *rdp;
> +
> +	WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
> +	debug_rcu_head_queue(head);
> +	head->func = func;
> +	head->next = NULL;
> +
> +	smp_mb(); /* Ensure RCU update seen before callback registry. */
> +
> +	/*
> +	 * Opportunistically note grace-period endings and beginnings.
> +	 * Note that we might see a beginning right after we see an
> +	 * end, but never vice versa, since this CPU has to pass through
> +	 * a quiescent state betweentimes.
> +	 */
> +	local_irq_save(flags);
> +	rdp = this_cpu_ptr(rsp->rda);
> +
> +	/* Add the callback to our list. */
> +	ACCESS_ONCE(rdp->qlen)++;
> +	if (lazy)
> +		rdp->qlen_lazy++;
> +	else
> +		rcu_idle_count_callbacks_posted();
> +	smp_mb();  /* Count before adding callback for rcu_barrier(). */
> +	*rdp->nxttail[RCU_NEXT_TAIL] = head;
> +	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
> +
> +	if (__is_kfree_rcu_offset((unsigned long)func))
> +		trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
> +					 rdp->qlen_lazy, rdp->qlen);
> +	else
> +		trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
> +
> +	/* Go handle any RCU core processing required. */
> +	__call_rcu_core(rsp, rdp, head, flags);
>  	local_irq_restore(flags);
>  }
>  
> -- 
> 1.7.8
>