[dm-devel] [PATCH 03/13] dm-mpath: Delay requeuing while path initialization is in progress

[Hannes Reinecke]

On 04/26/2017 08:37 PM, Bart Van Assche wrote:
> Requeuing a request immediately while path initialization is ongoing
> causes high CPU usage, something that is undesired. Hence delay
> requeuing while path initialization is in progress.
> 
> Signed-off-by: Bart Van Assche <bart.vanassche at sandisk.com>
> Cc: Hannes Reinecke <hare at suse.com>
> Cc: Christoph Hellwig <hch at lst.de>
> Cc: <stable at vger.kernel.org>
> ---
>  drivers/md/dm-mpath.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
> index 6d4333fdddf5..e38c92178746 100644
> --- a/drivers/md/dm-mpath.c
> +++ b/drivers/md/dm-mpath.c
> @@ -322,13 +322,16 @@ static int __pg_init_all_paths(struct multipath *m)
>  	return atomic_read(&m->pg_init_in_progress);
>  }
>  
> -static void pg_init_all_paths(struct multipath *m)
> +static int pg_init_all_paths(struct multipath *m)
>  {
>  	unsigned long flags;
> +	int ret;
>  
>  	spin_lock_irqsave(&m->lock, flags);
> -	__pg_init_all_paths(m);
> +	ret = __pg_init_all_paths(m);
>  	spin_unlock_irqrestore(&m->lock, flags);
> +
> +	return ret;
>  }
>  
>  static void __switch_pg(struct multipath *m, struct priority_group *pg)
> @@ -485,7 +488,6 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
>  				   struct request **__clone)
>  {
>  	struct multipath *m = ti->private;
> -	int r = DM_MAPIO_REQUEUE;
>  	size_t nr_bytes = blk_rq_bytes(rq);
>  	struct pgpath *pgpath;
>  	struct block_device *bdev;
> @@ -504,8 +506,8 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
>  		return -EIO;	/* Failed */
>  	} else if (test_bit(MPATHF_QUEUE_IO, &m->flags) ||
>  		   test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) {
> -		pg_init_all_paths(m);
> -		return r;
> +		return pg_init_all_paths(m) == 0 ? DM_MAPIO_REQUEUE :
> +			DM_MAPIO_DELAY_REQUEUE;
>  	}
>  
>  	memset(mpio, 0, sizeof(*mpio));
> 
Reviewed-by: Hannes Reinecke <hare at suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare at suse.de			               +49 911 74053 688
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