Re: [PATCH] Add a tracepoint for block request remapping

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

CC to Li

Li, What do you think?


> Since 2.6.31 now has request-based device-mapper, it's useful to have
> a tracepoint for request-remapping as well as bio-remapping.
> 
> This patch adds a tracepoint for request-remapping, trace_block_rq_remap().
> Existing trace_block_remap() is left unchanged but it might be better to
> rename it to trace_block_bio_remap().
> 
> Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> Cc: Jens Axboe <jens.axboe@oracle.com>
> Cc: Alasdair G Kergon <agk@redhat.com>
> ---
>  block/blk-core.c             |   11 +++++-----
>  drivers/md/dm.c              |    6 +++--
>  include/trace/events/block.h |   35 +++++++++++++++++++++++++++++++++-
>  kernel/trace/blktrace.c      |   44 ++++++++++++++++++++++++++++++++++++++-----
>  4 files changed, 83 insertions(+), 13 deletions(-)
> 
> Index: linux-2.6.31/block/blk-core.c
> ===================================================================
> --- linux-2.6.31.orig/block/blk-core.c
> +++ linux-2.6.31/block/blk-core.c
> @@ -34,6 +34,7 @@
>  #include "blk.h"
>  
>  EXPORT_TRACEPOINT_SYMBOL_GPL(block_remap);
> +EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
>  EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);
>  
>  static int __make_request(struct request_queue *q, struct bio *bio);
> Index: linux-2.6.31/drivers/md/dm.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/md/dm.c
> +++ linux-2.6.31/drivers/md/dm.c
> @@ -1503,6 +1503,8 @@ static void map_request(struct dm_target
>  		break;
>  	case DM_MAPIO_REMAPPED:
>  		/* The target has remapped the I/O so dispatch it */
> +		trace_block_rq_remap(clone->q, clone, disk_devt(dm_disk(md)),
> +				     blk_rq_pos(tio->orig));
>  		dm_dispatch_request(clone);
>  		break;
>  	case DM_MAPIO_REQUEUE:
> Index: linux-2.6.31/include/trace/events/block.h
> ===================================================================
> --- linux-2.6.31.orig/include/trace/events/block.h
> +++ linux-2.6.31/include/trace/events/block.h
> @@ -486,6 +486,39 @@ TRACE_EVENT(block_remap,
>  		  (unsigned long long)__entry->old_sector)
>  );
>  
> +TRACE_EVENT(block_rq_remap,
> +
> +	TP_PROTO(struct request_queue *q, struct request *rq, dev_t dev,
> +		 sector_t from),
> +
> +	TP_ARGS(q, rq, dev, from),
> +
> +	TP_STRUCT__entry(
> +		__field( dev_t,		dev		)
> +		__field( sector_t,	sector		)
> +		__field( unsigned int,	nr_sector	)
> +		__field( dev_t,		old_dev		)
> +		__field( sector_t,	old_sector	)
> +		__array( char,		rwbs,	6	)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->dev		= disk_devt(rq->rq_disk);
> +		__entry->sector		= blk_rq_pos(rq);
> +		__entry->nr_sector	= blk_rq_sectors(rq);
> +		__entry->old_dev	= dev;
> +		__entry->old_sector	= from;
> +		blk_fill_rwbs_rq(__entry->rwbs, rq);
> +	),
> +
> +	TP_printk("%d,%d %s %llu + %u <- (%d,%d) %llu",
> +		  MAJOR(__entry->dev), MINOR(__entry->dev), __entry->rwbs,
> +		  (unsigned long long)__entry->sector,
> +		  __entry->nr_sector,
> +		  MAJOR(__entry->old_dev), MINOR(__entry->old_dev),
> +		  (unsigned long long)__entry->old_sector)
> +);
> +
>  #endif /* _TRACE_BLOCK_H */
>  
>  /* This part must be outside protection */
> Index: linux-2.6.31/kernel/trace/blktrace.c
> ===================================================================
> --- linux-2.6.31.orig/kernel/trace/blktrace.c
> +++ linux-2.6.31/kernel/trace/blktrace.c
> @@ -852,6 +852,37 @@ static void blk_add_trace_remap(struct r
>  }
>  
>  /**
> + * blk_add_trace_rq_remap - Add a trace for a request-remap operation
> + * @q:		queue the io is for
> + * @rq:		the source request
> + * @dev:	target device
> + * @from:	source sector
> + *
> + * Description:
> + *     Device mapper remaps request to other devices.
> + *     Add a trace for that action.
> + *
> + **/
> +static void blk_add_trace_rq_remap(struct request_queue *q,
> +				   struct request *rq, dev_t dev,
> +				   sector_t from)
> +{
> +	struct blk_trace *bt = q->blk_trace;
> +	struct blk_io_trace_remap r;
> +
> +	if (likely(!bt))
> +		return;
> +
> +	r.device_from = cpu_to_be32(dev);
> +	r.device_to   = disk_devt(rq->rq_disk);
> +	r.sector_from = cpu_to_be64(from);
> +
> +	__blk_add_trace(bt, blk_rq_pos(rq), blk_rq_bytes(rq),
> +			rq_data_dir(rq), BLK_TA_REMAP, !!rq->errors,
> +			sizeof(r), &r);
> +}
> +
> +/**
>   * blk_add_driver_data - Add binary message with driver-specific data
>   * @q:		queue the io is for
>   * @rq:		io request
> @@ -918,10 +949,13 @@ static void blk_register_tracepoints(voi
>  	WARN_ON(ret);
>  	ret = register_trace_block_remap(blk_add_trace_remap);
>  	WARN_ON(ret);
> +	ret = register_trace_block_rq_remap(blk_add_trace_rq_remap);
> +	WARN_ON(ret);
>  }
>  
>  static void blk_unregister_tracepoints(void)
>  {
> +	unregister_trace_block_rq_remap(blk_add_trace_rq_remap);
>  	unregister_trace_block_remap(blk_add_trace_remap);
>  	unregister_trace_block_split(blk_add_trace_split);
>  	unregister_trace_block_unplug_io(blk_add_trace_unplug_io);
> --
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