Re: [PATCH v2] zbd: fix sequential write pattern with verify= and max_open_zones=

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On 2020/04/14 3:52, Alexey Dobriyan wrote:
> Sequential write with max_open_zones=1 has interesting (read: buggy)
> interaction with verify=.
> 
> If verify is off, then job runs correctly and IO is sequential,
> and restarted from offset 0 and remains sequential.
> 
> If verify is on, then 1 full run is done and verified correctly.
> At this point there is exactly 1 open zone which is the last zone.
> 
> Now IO restarts from offset 0 and pick_random_zone() picks opened zone
> #0 which is the last zone because offset is 0. All IO is redirected
> to the last zone, which is rewritten once triggering verify again.
> 
> IO pattern becomes: 1 full sequential rewrite followed by constant
> sequential rewrites of the last zone.
> 
> 
> 	[global]
> 	filename=/dev/loop0
> 	direct=1
> 	zonemode=zbd
> 	zonesize=1M
> 	bs=512K
> 	rw=write
> 	verify=xxhash
> 	[j]
> 	max_open_zones=1
> 	io_size=3G
> 
> Fix is to close every zone given that verification acts as a barrier
> between jobs.
> 
> max_open_zones=2 can restart from half of the device, etc.
> 
> Signed-off-by: Alexey Dobriyan (SK hynix) <adobriyan@xxxxxxxxx>

Looks good to me.

Reviewed-by: Damien Le Moal <damien.lemoal@xxxxxxx>

> ---
> 
>  zbd.c |   52 +++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 33 insertions(+), 19 deletions(-)
> 
> --- a/zbd.c
> +++ b/zbd.c
> @@ -687,6 +687,22 @@ static int zbd_reset_zone(struct thread_data *td, struct fio_file *f,
>  	return zbd_reset_range(td, f, z->start, (z+1)->start - z->start);
>  }
>  
> +/* The caller must hold f->zbd_info->mutex */
> +static void zbd_close_zone(struct thread_data *td, const struct fio_file *f,
> +			   unsigned int open_zone_idx)
> +{
> +	uint32_t zone_idx;
> +
> +	assert(open_zone_idx < f->zbd_info->num_open_zones);
> +	zone_idx = f->zbd_info->open_zones[open_zone_idx];
> +	memmove(f->zbd_info->open_zones + open_zone_idx,
> +		f->zbd_info->open_zones + open_zone_idx + 1,
> +		(ZBD_MAX_OPEN_ZONES - (open_zone_idx + 1)) *
> +		sizeof(f->zbd_info->open_zones[0]));
> +	f->zbd_info->num_open_zones--;
> +	f->zbd_info->zone_info[zone_idx].open = 0;
> +}
> +
>  /*
>   * Reset a range of zones. Returns 0 upon success and 1 upon failure.
>   * @td: fio thread data.
> @@ -710,12 +726,26 @@ static int zbd_reset_zones(struct thread_data *td, struct fio_file *f,
>  	dprint(FD_ZBD, "%s: examining zones %u .. %u\n", f->file_name,
>  		zbd_zone_nr(f->zbd_info, zb), zbd_zone_nr(f->zbd_info, ze));
>  	for (z = zb; z < ze; z++) {
> +		uint32_t nz = z - f->zbd_info->zone_info;
> +
>  		if (!zbd_zone_swr(z))
>  			continue;
>  		zone_lock(td, z);
> -		reset_wp = all_zones ? z->wp != z->start :
> -				(td->o.td_ddir & TD_DDIR_WRITE) &&
> -				z->wp % min_bs != 0;
> +		if (all_zones) {
> +			unsigned int i;
> +
> +			pthread_mutex_lock(&f->zbd_info->mutex);
> +			for (i = 0; i < f->zbd_info->num_open_zones; i++) {
> +				if (f->zbd_info->open_zones[i] == nz)
> +					zbd_close_zone(td, f, i);
> +			}
> +			pthread_mutex_unlock(&f->zbd_info->mutex);
> +
> +			reset_wp = z->wp != z->start;
> +		} else {
> +			reset_wp = (td->o.td_ddir & TD_DDIR_WRITE) &&
> +					z->wp % min_bs != 0;
> +		}
>  		if (reset_wp) {
>  			dprint(FD_ZBD, "%s: resetting zone %u\n",
>  			       f->file_name,
> @@ -905,22 +935,6 @@ out:
>  	return res;
>  }
>  
> -/* The caller must hold f->zbd_info->mutex */
> -static void zbd_close_zone(struct thread_data *td, const struct fio_file *f,
> -			   unsigned int open_zone_idx)
> -{
> -	uint32_t zone_idx;
> -
> -	assert(open_zone_idx < f->zbd_info->num_open_zones);
> -	zone_idx = f->zbd_info->open_zones[open_zone_idx];
> -	memmove(f->zbd_info->open_zones + open_zone_idx,
> -		f->zbd_info->open_zones + open_zone_idx + 1,
> -		(ZBD_MAX_OPEN_ZONES - (open_zone_idx + 1)) *
> -		sizeof(f->zbd_info->open_zones[0]));
> -	f->zbd_info->num_open_zones--;
> -	f->zbd_info->zone_info[zone_idx].open = 0;
> -}
> -
>  /* Anything goes as long as it is not a constant. */
>  static uint32_t pick_random_zone_idx(const struct fio_file *f,
>  				     const struct io_u *io_u)
> 


-- 
Damien Le Moal
Western Digital Research




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