linux-kernel - Re: [PATCH] dm mpath: fixup sched_clock() usage in historical selector

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Message-ID: <87wnfvxjtm.fsf@collabora.com>
Date:   Mon, 11 Apr 2022 19:48:53 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Khazhismel Kumykov <khazhy@...gle.com>
Cc:     Mike Snitzer <snitzer@...nel.org>,
        Alasdair Kergon <agk@...hat.com>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dm mpath: fixup sched_clock() usage in historical selector

Khazhismel Kumykov <khazhy@...gle.com> writes:

> mixing sched_clock() and ktime_get_ns() will give bad results, don't do
> it
>
> Fixes: 2613eab11996 ("dm mpath: add Historical Service Time Path Selector")
> Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>

Looks good.

Reviewed-by: Gabriel Krisman Bertazi <krisman@...labora.com>


> ---
>  drivers/md/dm-ps-historical-service-time.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/md/dm-ps-historical-service-time.c b/drivers/md/dm-ps-historical-service-time.c
> index 875bca30a0dd..82f2a06153dc 100644
> --- a/drivers/md/dm-ps-historical-service-time.c
> +++ b/drivers/md/dm-ps-historical-service-time.c
> @@ -27,7 +27,6 @@
>  #include <linux/blkdev.h>
>  #include <linux/slab.h>
>  #include <linux/module.h>
> -#include <linux/sched/clock.h>
>  
>  
>  #define DM_MSG_PREFIX	"multipath historical-service-time"
> @@ -433,7 +432,7 @@ static struct dm_path *hst_select_path(struct path_selector *ps,
>  {
>  	struct selector *s = ps->context;
>  	struct path_info *pi = NULL, *best = NULL;
> -	u64 time_now = sched_clock();
> +	u64 time_now = ktime_get_ns();
>  	struct dm_path *ret = NULL;
>  	unsigned long flags;
>  
> @@ -474,7 +473,7 @@ static int hst_start_io(struct path_selector *ps, struct dm_path *path,
>  
>  static u64 path_service_time(struct path_info *pi, u64 start_time)
>  {
> -	u64 sched_now = ktime_get_ns();
> +	u64 now = ktime_get_ns();
>  
>  	/* if a previous disk request has finished after this IO was
>  	 * sent to the hardware, pretend the submission happened
> @@ -483,11 +482,11 @@ static u64 path_service_time(struct path_info *pi, u64 start_time)
>  	if (time_after64(pi->last_finish, start_time))
>  		start_time = pi->last_finish;
>  
> -	pi->last_finish = sched_now;
> -	if (time_before64(sched_now, start_time))
> +	pi->last_finish = now;
> +	if (time_before64(now, start_time))
>  		return 0;
>  
> -	return sched_now - start_time;
> +	return now - start_time;
>  }
>  
>  static int hst_end_io(struct path_selector *ps, struct dm_path *path,

-- 
Gabriel Krisman Bertazi