Re: [RFC] block: add counter to track io request's d2c time

[Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>]

hi Jens Axboe,

Would you please have a look at his patch, thanks.

Regards,
Xiaoguang Wang

> Indeed tool iostat's await is not good enough, which is somewhat sketchy
> and could not show request's latency on device driver's side.
>
> Here we add a new counter to track io request's d2c time, also with this
> patch, we can extend iostat to show this value easily.
>
> Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
> ---
>   block/blk-core.c          | 3 +++
>   block/genhd.c             | 7 +++++--
>   block/partition-generic.c | 8 ++++++--
>   include/linux/genhd.h     | 4 ++++
>   4 files changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index ee1b35fe8572..b0449ec80a7d 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1257,6 +1257,9 @@ void blk_account_io_done(struct request *req, u64 now)
>   		update_io_ticks(part, jiffies);
>   		part_stat_inc(part, ios[sgrp]);
>   		part_stat_add(part, nsecs[sgrp], now - req->start_time_ns);
> +		if (req->io_start_time_ns)
> +			part_stat_add(part, d2c_nsecs[sgrp],
> +				      now - req->io_start_time_ns);
>   		part_stat_add(part, time_in_queue, nsecs_to_jiffies64(now - req->start_time_ns));
>   		part_dec_in_flight(req->q, part, rq_data_dir(req));
>   
> diff --git a/block/genhd.c b/block/genhd.c
> index 24654e1d83e6..727bc1de1a74 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -1377,7 +1377,7 @@ static int diskstats_show(struct seq_file *seqf, void *v)
>   			   "%lu %lu %lu %u "
>   			   "%lu %lu %lu %u "
>   			   "%u %u %u "
> -			   "%lu %lu %lu %u\n",
> +			   "%lu %lu %lu %u %u %u %u\n",
>   			   MAJOR(part_devt(hd)), MINOR(part_devt(hd)),
>   			   disk_name(gp, hd->partno, buf),
>   			   part_stat_read(hd, ios[STAT_READ]),
> @@ -1394,7 +1394,10 @@ static int diskstats_show(struct seq_file *seqf, void *v)
>   			   part_stat_read(hd, ios[STAT_DISCARD]),
>   			   part_stat_read(hd, merges[STAT_DISCARD]),
>   			   part_stat_read(hd, sectors[STAT_DISCARD]),
> -			   (unsigned int)part_stat_read_msecs(hd, STAT_DISCARD)
> +			   (unsigned int)part_stat_read_msecs(hd, STAT_DISCARD),
> +			   (unsigned int)part_stat_read_d2c_msecs(hd, STAT_READ),
> +			   (unsigned int)part_stat_read_d2c_msecs(hd, STAT_WRITE),
> +			   (unsigned int)part_stat_read_d2c_msecs(hd, STAT_DISCARD)
>   			);
>   	}
>   	disk_part_iter_exit(&piter);
> diff --git a/block/partition-generic.c b/block/partition-generic.c
> index aee643ce13d1..0635a46a31dd 100644
> --- a/block/partition-generic.c
> +++ b/block/partition-generic.c
> @@ -127,7 +127,7 @@ ssize_t part_stat_show(struct device *dev,
>   		"%8lu %8lu %8llu %8u "
>   		"%8lu %8lu %8llu %8u "
>   		"%8u %8u %8u "
> -		"%8lu %8lu %8llu %8u"
> +		"%8lu %8lu %8llu %8u %8u %8u %8u %8u"
>   		"\n",
>   		part_stat_read(p, ios[STAT_READ]),
>   		part_stat_read(p, merges[STAT_READ]),
> @@ -143,7 +143,11 @@ ssize_t part_stat_show(struct device *dev,
>   		part_stat_read(p, ios[STAT_DISCARD]),
>   		part_stat_read(p, merges[STAT_DISCARD]),
>   		(unsigned long long)part_stat_read(p, sectors[STAT_DISCARD]),
> -		(unsigned int)part_stat_read_msecs(p, STAT_DISCARD));
> +		(unsigned int)part_stat_read_msecs(p, STAT_DISCARD),
> +		(unsigned int)part_stat_read_msecs(p, STAT_DISCARD),
> +		(unsigned int)part_stat_read_d2c_msecs(p, STAT_READ),
> +		(unsigned int)part_stat_read_d2c_msecs(p, STAT_WRITE),
> +		(unsigned int)part_stat_read_d2c_msecs(p, STAT_DISCARD));
>   }
>   
>   ssize_t part_inflight_show(struct device *dev, struct device_attribute *attr,
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 8b5330dd5ac0..f80ba947cac2 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -85,6 +85,7 @@ struct partition {
>   
>   struct disk_stats {
>   	u64 nsecs[NR_STAT_GROUPS];
> +	u64 d2c_nsecs[NR_STAT_GROUPS];
>   	unsigned long sectors[NR_STAT_GROUPS];
>   	unsigned long ios[NR_STAT_GROUPS];
>   	unsigned long merges[NR_STAT_GROUPS];
> @@ -367,6 +368,9 @@ static inline void free_part_stats(struct hd_struct *part)
>   #define part_stat_read_msecs(part, which)				\
>   	div_u64(part_stat_read(part, nsecs[which]), NSEC_PER_MSEC)
>   
> +#define part_stat_read_d2c_msecs(part, which)				\
> +	div_u64(part_stat_read(part, d2c_nsecs[which]), NSEC_PER_MSEC)
> +
>   #define part_stat_read_accum(part, field)				\
>   	(part_stat_read(part, field[STAT_READ]) +			\
>   	 part_stat_read(part, field[STAT_WRITE]) +			\