Re: Slow dc3dd in 3.18 on x86

["Michael L. Semon" <mlsemon35@gmail.com>]

On 10/24/14 21:51, Martin K. Petersen wrote:
>>>>>> "Michael" == Michael L Semon <mlsemon35@gmail.com> writes:
>
> Michael> There was nothing regarding integrity in /sys/block/sda.  I was
> Michael> under the impression that both bio integrity and T10 checksums
> Michael> require hardware support from good hardware, so the config
> Michael> items have always been shut off.
>
> That's correct. But I see what's going on.
>
> Please try this:
>
> commit 8d331952d2cd341d5c0e64eee961f78f6eb4b968
> Author: Martin K. Petersen <martin.petersen@oracle.com>
> Date:   Fri Oct 24 21:39:12 2014 -0400
>
>      block: Fix merge logic when CONFIG_BLK_DEV_INTEGRITY is not defined
>
>      Commit 4eaf99beadce switched to returning bool and as a result
>      reversed the logic of the integrity merge checks.  However, the
>      empty stubs used when the block integrity code is compiled out were
>      still returning 0. Make these stubs return "true".
>
>      Reported-by: Michael L. Semon <mlsemon35@gmail.com>
>      Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 9fbf4d3196ed..7442c6b9187e 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1590,13 +1590,13 @@ static inline bool blk_integrity_merge_rq(struct request_queue *rq,
>   					  struct request *r1,
>   					  struct request *r2)
>   {
> -	return 0;
> +	return true;
>   }
>   static inline bool blk_integrity_merge_bio(struct request_queue *rq,
>   					   struct request *r,
>   					   struct bio *b)
>   {
> -	return 0;
> +	return true;
>   }
>   static inline bool blk_integrity_is_initialized(struct gendisk *g)
>   {
>

Excellent!  All is well with the problem kernel.  All is well with the
night's git master + xfs-oss/for-next as well.  The saved E-mail patched
cleanly against both kernels using `git am`.  About 40 GB of data was
written, some using fio, most using dc3dd.  No problems.

I'll keep this patch and stand behind its good results so far.

Thanks again!

Michael