This is good idea.
Mikulas
On Fri, 13 Sep 2013, Jun'ichi Nomura wrote:
> Other approach might be putting the info on tracepoints.
> Then the tracepoint framework will take care of the static_key thing.
>
> Since 'the number of bios in a request' is a block-layer generic info,
> you could extend the block layer events instead of having your own.
>
> Attached patch adds it to block_rq_remap event.
> You could do something like this to see requests with many bios:
> echo 'nr_bios > 32' > /sys/kernel/debug/tracing/events/block/block_rq_remap/filter
> echo 1 > /sys/kernel/debug/tracing/events/block/block_rq_remap/enable
>
> For example,
> kworker/1:1H-308 [001] d..1 276.242448: block_rq_remap: 8,64 W 1967760 + 512 <- (253,1) 1967760 64
> kworker/1:1H-308 [001] d..1 276.242482: block_rq_remap: 8,160 W 1968272 + 512 <- (253,1) 1968272 64
> kworker/1:1H-308 [001] d..1 276.242515: block_rq_remap: 65,0 W 1968784 + 512 <- (253,1) 1968784 64
> # the last item in line is the number of bios. ("64" in this case)
>
> ---
> Jun'ichi Nomura, NEC Corporation
>
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 2fdb4a4..0e6f765 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -862,6 +862,17 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq)
> return blk_queue_get_max_sectors(q, rq->cmd_flags);
> }
>
> +static inline unsigned int blk_rq_count_bios(struct request *rq)
> +{
> + unsigned int nr_bios = 0;
> + struct bio *bio;
> +
> + __rq_for_each_bio(bio, rq)
> + nr_bios++;
> +
> + return nr_bios;
> +}
> +
> /*
> * Request issue related functions.
> */
> diff --git a/include/trace/events/block.h b/include/trace/events/block.h
> index 60ae7c3..4c2301d 100644
> --- a/include/trace/events/block.h
> +++ b/include/trace/events/block.h
> @@ -618,6 +618,7 @@ TRACE_EVENT(block_rq_remap,
> __field( unsigned int, nr_sector )
> __field( dev_t, old_dev )
> __field( sector_t, old_sector )
> + __field( unsigned int, nr_bios )
> __array( char, rwbs, RWBS_LEN)
> ),
>
> @@ -627,15 +628,16 @@ TRACE_EVENT(block_rq_remap,
> __entry->nr_sector = blk_rq_sectors(rq);
> __entry->old_dev = dev;
> __entry->old_sector = from;
> + __entry->nr_bios = blk_rq_count_bios(rq);
> blk_fill_rwbs(__entry->rwbs, rq->cmd_flags, blk_rq_bytes(rq));
> ),
>
> - TP_printk("%d,%d %s %llu + %u <- (%d,%d) %llu",
> + TP_printk("%d,%d %s %llu + %u <- (%d,%d) %llu %u",
> 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)
> + (unsigned long long)__entry->old_sector, __entry->nr_bios)
> );
>
> #endif /* _TRACE_BLOCK_H */
>
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