Re: [PATCH 0/2] Change type-2 dif to use rq embedded 32 byte cdb

[Rob Evers <revers@redhat.com>]

cc Lukasz and Maciej from Intel and changing Dan William's email


On 11/21/2012 03:07 PM, Rob Evers wrote:
> These patches replace the original t10 type 2 dif mempool implementation
> by increasing the block and scsi cdb maximum sizes from 16 to 32 bytes.
> The cdb embedded in the request structure can then be used for type 2
> dif commands, or other 32 byte cdbs as required.
>
> Motivation for this is that type-2 dif commands should be treated as
> any other read/writes generally, without any performance penalty.
>
> This patch set conflicts with a patch previously posted which addresses
> a race in UA induced retries with type 2 dif commands.  These patches also
> address that problem:
>
> http://marc.info/?l=linux-scsi&m=135186352200668&w=2
>
> Testing:
>
> Readily reproduced the race condition panic by simultaneously
> inducing UAs while load testing 8 scsi_debug devices.  With patch
> applied, same testing ran for 15 hours without a panic.
>
> Sanity tested performance using scsi_debug, with and without
> type 2 dif enabled.  Order 80% performance increase noticed
> with patches when scsi_debug was running in dif type 2 mode.
> Running scsi_debug without type 2 dif, performance was approximately
> equal.
>
> Used 3.7.0-rc5 for testing and patch generation.
>
> root (2):
>    Change the cdb size limits in block and scsi to 32 bytes
>    Change dif type 2 commands to use embedded 32 byte cdb
>
>   drivers/scsi/sd.c        | 45 +--------------------------------------------
>   drivers/scsi/sd.h        |  5 -----
>   include/linux/blkdev.h   |  2 +-
>   include/scsi/scsi_cmnd.h | 13 ++-----------
>   4 files changed, 4 insertions(+), 61 deletions(-)
>