Re: [PATCH 1/2] Revert "block: remove artifical max_hw_sectors cap"

[Ed Cashin <ed.cashin@acm.org>]

ACK.

On 08/13/2015 02:57 PM, Jeff Moyer wrote:
> This reverts commit 34b48db66e08ca1c1bc07cf305d672ac940268dc.
> That commit caused performance regressions for streaming I/O
> workloads on a number of different storage devices, from
> SATA disks to external RAID arrays.  It also managed to
> trip up some buggy firmware in at least one drive, causing
> data corruption.
>
> The next patch will bump the default max_sectors_kb value to
> 1280, which will accommodate a 10-data-disk stripe write
> with chunk size 128k.  In the testing I've done using iozone,
> fio, and aio-stress, a value of 1280 does not show a big
> performance difference from 512.  This will hopefully still
> help the software RAID setup that Christoph saw the original
> performance gains with while still not regressing other
> storage configurations.
>
> Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
> ---
>   block/blk-settings.c       | 4 +++-
>   drivers/block/aoe/aoeblk.c | 2 +-
>   include/linux/blkdev.h     | 1 +
>   3 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-settings.c b/block/blk-settings.c
> index 12600bf..b160f89 100644
> --- a/block/blk-settings.c
> +++ b/block/blk-settings.c
> @@ -257,7 +257,9 @@ void blk_limits_max_hw_sectors(struct queue_limits *limits, unsigned int max_hw_
>   		       __func__, max_hw_sectors);
>   	}
>   
> -	limits->max_sectors = limits->max_hw_sectors = max_hw_sectors;
> +	limits->max_hw_sectors = max_hw_sectors;
> +	limits->max_sectors = min_t(unsigned int, max_hw_sectors,
> +				    BLK_DEF_MAX_SECTORS);
>   }
>   EXPORT_SYMBOL(blk_limits_max_hw_sectors);
>   
> diff --git a/drivers/block/aoe/aoeblk.c b/drivers/block/aoe/aoeblk.c
> index 46c282f..dd73e1f 100644
> --- a/drivers/block/aoe/aoeblk.c
> +++ b/drivers/block/aoe/aoeblk.c
> @@ -395,7 +395,7 @@ aoeblk_gdalloc(void *vp)
>   	WARN_ON(d->flags & DEVFL_TKILL);
>   	WARN_ON(d->gd);
>   	WARN_ON(d->flags & DEVFL_UP);
> -	blk_queue_max_hw_sectors(q, 1024);
> +	blk_queue_max_hw_sectors(q, BLK_DEF_MAX_SECTORS);
>   	q->backing_dev_info.name = "aoe";
>   	q->backing_dev_info.ra_pages = READ_AHEAD / PAGE_CACHE_SIZE;
>   	d->bufpool = mp;
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index d4068c1..1fd459e1 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1138,6 +1138,7 @@ extern int blk_verify_command(unsigned char *cmd, fmode_t has_write_perm);
>   enum blk_default_limits {
>   	BLK_MAX_SEGMENTS	= 128,
>   	BLK_SAFE_MAX_SECTORS	= 255,
> +	BLK_DEF_MAX_SECTORS	= 1024,
>   	BLK_MAX_SEGMENT_SIZE	= 65536,
>   	BLK_SEG_BOUNDARY_MASK	= 0xFFFFFFFFUL,
>   };