Slower write performance in RHEL6

Slower write performance in RHEL6

[Li Liu]

Dear all,

    In RHEL6(linux-2.6.32-71.el6), I added some codes in
scsi_softirq_done to check the result of execute scsi commands:
WRITE_6, WRITE_10, WRITE_12, WRITE_16 when I executed "dd if=/dev/zero
of=/dev/xda bs=64k count=10000". I found a lot of write error messages
in scsi_softirq_done, the disposition(variable) was ADD_TO_MLQUEUE and
the speed was 78MB/s.
    Then I changed MPT_SCSI_CMD_PER_DEV_HIGH from 64 to 32 in
mptscsih_change_queue_depth, the speed was 140MB/s and none error
messages.
    * /dev/xda is a scsi disk.
    * the scsi host is LSI1064E.
    * MPT_SCSI_CMD_PER_DEV_HIGH will be assigned to blk_queue_tag->max_depth.

    My questions are:
    Is the TCQ depth limited by hard disk, how can I get the limited?
    Why the speed was drop to 78MB/s when MPT_SCSI_CMD_PER_DEV_HIGH was 64?
    Could I change MPT_SCSI_CMD_PER_DEV_HIGH to 32 or 16 or 8, Will it
cause any problem?

    Thanks for any ideas.

Thanks,
Alex Liu

Re: Slower write performance in RHEL6

[Ric Wheeler]

On 07/26/2011 07:22 AM, Li Liu wrote:
> Dear all,
>
>      In RHEL6(linux-2.6.32-71.el6), I added some codes in
> scsi_softirq_done to check the result of execute scsi commands:
> WRITE_6, WRITE_10, WRITE_12, WRITE_16 when I executed "dd if=/dev/zero
> of=/dev/xda bs=64k count=10000". I found a lot of write error messages
> in scsi_softirq_done, the disposition(variable) was ADD_TO_MLQUEUE and
> the speed was 78MB/s.
>      Then I changed MPT_SCSI_CMD_PER_DEV_HIGH from 64 to 32 in
> mptscsih_change_queue_depth, the speed was 140MB/s and none error
> messages.
>      * /dev/xda is a scsi disk.
>      * the scsi host is LSI1064E.
>      * MPT_SCSI_CMD_PER_DEV_HIGH will be assigned to blk_queue_tag->max_depth.
>
>      My questions are:
>      Is the TCQ depth limited by hard disk, how can I get the limited?
>      Why the speed was drop to 78MB/s when MPT_SCSI_CMD_PER_DEV_HIGH was 64?
>      Could I change MPT_SCSI_CMD_PER_DEV_HIGH to 32 or 16 or 8, Will it
> cause any problem?
>
>      Thanks for any ideas.
>
> Thanks,
> Alex Liu

When you have a vendor specific issues, it is probably best to raise a ticket 
with the vendor's support organization....

Thanks!

Ric