[Devel] [PATCH VZ10 01/11] drivers/md/dm-rq: fix time accounting for request-based dm drivers

[Vasileios Almpanis]

On 7/13/26 2:36 AM, Andrey Zhadchenko wrote:
> Currently all requests for request-based dm drivers are falling in
> the last bin for both normal and precise counting due to incorrect
> calculations.
>
> Ordinary counting expects that start_time passed to dm_stats_account_io()
> is an absolute value and substracts it from jiffies to get request time.
> However rq_end_stats() calculates and passes request duration. So we
> actually get jiffies - <request_duration_in_jiffies>, which is incorrect.
> rq_end_stats() should not do the substraction.
>
> For precise calulation stats->aux_duration_ns is used. It is calculated
> in dm_stats_account_io() like that:
> stats_aux->duration_ns = ktime_to_ns(ktime_get()) - stats_aux->duration_ns;
> The problem is that stats_aux->duration_ns() is set by
> dm_stats_record_start() which is called only for bio-based targets.
> It should also be called in dm_start_request().
>
> https://virtuozzo.atlassian.net/browse/VSTOR-103846
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
Did you forget Fixes: tag?
Something like Fixes: e262f3474152 ("dm stats: add support for 
request-based DM devices")
> ---
>   drivers/md/dm-rq.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
> index 2177666c64f32..58ad4c94d6119 100644
> --- a/drivers/md/dm-rq.c
> +++ b/drivers/md/dm-rq.c
> @@ -129,7 +129,6 @@ static void rq_end_stats(struct mapped_device *md, struct request *orig)
>   	if (unlikely(dm_stats_used(&md->stats))) {
>   		struct dm_rq_target_io *tio = tio_from_request(orig);
>   
> -		tio->duration_jiffies = jiffies - tio->duration_jiffies;
>   		dm_stats_account_io(&md->stats, rq_data_dir(orig),
>   				    blk_rq_pos(orig), tio->n_sectors, true,
>   				    tio->duration_jiffies, &tio->stats_aux);
> @@ -448,6 +447,8 @@ static void dm_start_request(struct mapped_device *md, struct request *orig)
>   
>   		tio->duration_jiffies = jiffies;
>   		tio->n_sectors = blk_rq_sectors(orig);
> +
> +		dm_stats_record_start(&md->stats, &tio->stats_aux);
>   		dm_stats_account_io(&md->stats, rq_data_dir(orig),
>   				    blk_rq_pos(orig), tio->n_sectors, false, 0,
>   				    &tio->stats_aux);

-- 
Best regards, Vasileios Almpanis
Software Developer, Virtuozzo.