Subject: Re: [PATCH v4 2/9] net: rds: use this_cpu_* per-cpu helper

From: Shan Wei <[email-masked]>
Date: Fri, 16 Nov 2012 16:38:33 +0800

Shan Wei said, at 2012/11/13 9:52:
> From: Shan Wei <[email-masked]>
> 
> 
> Signed-off-by: Shan Wei <[email-masked]>
> Reviewed-by: Christoph Lameter <[email-masked]>

David Miller,  would you like to pick it up to your net-next tree?

> ---
> v4:
> 1. add missing __percpu annotations.
> 2. [read|write]ing fields of struct rds_ib_cache_head
> using __this_cpu_* operation, drop per_cpu_ptr.
> ---
>  net/rds/ib.h      |    2 +-
>  net/rds/ib_recv.c |   24 +++++++++++++-----------
>  2 files changed, 14 insertions(+), 12 deletions(-)
> 
> diff --git a/net/rds/ib.h b/net/rds/ib.h
> index 8d2b3d5..7280ab8 100644
> --- a/net/rds/ib.h
> +++ b/net/rds/ib.h
> @@ -50,7 +50,7 @@ struct rds_ib_cache_head {
>  };
>  
>  struct rds_ib_refill_cache {
> -	struct rds_ib_cache_head *percpu;
> +	struct rds_ib_cache_head __percpu *percpu;
>  	struct list_head	 *xfer;
>  	struct list_head	 *ready;
>  };
> diff --git a/net/rds/ib_recv.c b/net/rds/ib_recv.c
> index 8d19491..8c5bc85 100644
> --- a/net/rds/ib_recv.c
> +++ b/net/rds/ib_recv.c
> @@ -418,20 +418,21 @@ static void rds_ib_recv_cache_put(struct list_head *new_item,
>  				 struct rds_ib_refill_cache *cache)
>  {
>  	unsigned long flags;
> -	struct rds_ib_cache_head *chp;
>  	struct list_head *old;
> +	struct list_head __percpu *chpfirst;
>  
>  	local_irq_save(flags);
>  
> -	chp = per_cpu_ptr(cache->percpu, smp_processor_id());
> -	if (!chp->first)
> +	chpfirst = __this_cpu_read(cache->percpu->first);
> +	if (!chpfirst)
>  		INIT_LIST_HEAD(new_item);
>  	else /* put on front */
> -		list_add_tail(new_item, chp->first);
> -	chp->first = new_item;
> -	chp->count++;
> +		list_add_tail(new_item, chpfirst);
>  
> -	if (chp->count < RDS_IB_RECYCLE_BATCH_COUNT)
> +	__this_cpu_write(chpfirst, new_item);
> +	__this_cpu_inc(cache->percpu->count);
> +
> +	if (__this_cpu_read(cache->percpu->count) < RDS_IB_RECYCLE_BATCH_COUNT)
>  		goto end;
>  
>  	/*
> @@ -443,12 +444,13 @@ static void rds_ib_recv_cache_put(struct list_head *new_item,
>  	do {
>  		old = xchg(&cache->xfer, NULL);
>  		if (old)
> -			list_splice_entire_tail(old, chp->first);
> -		old = cmpxchg(&cache->xfer, NULL, chp->first);
> +			list_splice_entire_tail(old, chpfirst);
> +		old = cmpxchg(&cache->xfer, NULL, chpfirst);
>  	} while (old);
>  
> -	chp->first = NULL;
> -	chp->count = 0;
> +
> +	__this_cpu_write(chpfirst, NULL);
> +	__this_cpu_write(cache->percpu->count, 0);
>  end:
>  	local_irq_restore(flags);
>  }
>