Re: [PATCH tip/core/rcu 6/7] rcu: Move early-boot callbacks to no-CBs lists for no-CBs CPUs

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- Original Message -----
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> To: linux-kernel@vger.kernel.org
> Cc: mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, "mathieu desnoyers"
> <mathieu.desnoyers@efficios.com>, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
> rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com,
> oleg@redhat.com, "bobby prani" <bobby.prani@gmail.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> Sent: Tuesday, March 3, 2015 11:45:47 AM
> Subject: [PATCH tip/core/rcu 6/7] rcu: Move early-boot callbacks to no-CBs lists for no-CBs CPUs
> 
> From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> 
> When a CPU is first determined to be a no-CBs CPUs, this commit causes
> any early boot callbacks to be moved to the no-CBs callback list,
> allowing them t obe invoked.
                ^^^^^
out-of-order space ;)

Thanks,

Mathieu

> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
>  kernel/rcu/tree.c        |  1 +
>  kernel/rcu/tree_plugin.h | 24 ++++++++++++------------
>  2 files changed, 13 insertions(+), 12 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 92fd3eab5823..0317bf7d997f 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2851,6 +2851,7 @@ __call_rcu(struct rcu_head *head, void (*func)(struct
> rcu_head *rcu),
>  		 * and then drop through to queue the callback.
>  		 */
>  		BUG_ON(cpu != -1);
> +		WARN_ON_ONCE(!rcu_is_watching());
>  		if (!likely(rdp->nxtlist))
>  			init_default_callback_list(rdp);
>  	}
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 75d5f096bcb0..afddd5641bea 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2393,18 +2393,8 @@ void __init rcu_init_nohz(void)
>  		pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
>  
>  	for_each_rcu_flavor(rsp) {
> -		for_each_cpu(cpu, rcu_nocb_mask) {
> -			struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
> -
> -			/*
> -			 * If there are early callbacks, they will need
> -			 * to be moved to the nocb lists.
> -			 */
> -			WARN_ON_ONCE(rdp->nxttail[RCU_NEXT_TAIL] !=
> -				     &rdp->nxtlist &&
> -				     rdp->nxttail[RCU_NEXT_TAIL] != NULL);
> -			init_nocb_callback_list(rdp);
> -		}
> +		for_each_cpu(cpu, rcu_nocb_mask)
> +			init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
>  		rcu_organize_nocb_kthreads(rsp);
>  	}
>  }
> @@ -2541,6 +2531,16 @@ static bool init_nocb_callback_list(struct rcu_data
> *rdp)
>  	if (!rcu_is_nocb_cpu(rdp->cpu))
>  		return false;
>  
> +	/* If there are early-boot callbacks, move them to nocb lists. */
> +	if (rdp->nxtlist) {
> +		rdp->nocb_head = rdp->nxtlist;
> +		rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL];
> +		atomic_long_set(&rdp->nocb_q_count, rdp->qlen);
> +		atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy);
> +		rdp->nxtlist = NULL;
> +		rdp->qlen = 0;
> +		rdp->qlen_lazy = 0;
> +	}
>  	rdp->nxttail[RCU_NEXT_TAIL] = NULL;
>  	return true;
>  }
> --
> 1.8.1.5
> 
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com