Re: [PATCH 0/2] scsi: revert two commits for avoiding host-wide host_busy counter for scsi_mq

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On 8/28/18 11:54 AM, Omar Sandoval wrote:
> On Mon, Aug 27, 2018 at 08:52:34AM -0600, Jens Axboe wrote:
>> On 8/27/18 1:24 AM, Ming Lei wrote:
>>> Hi,
>>>
>>> There is fundamental issue in commit 328728630d9f2bf1 (scsi: core: avoid
>>> host-wide host_busy counter for scsi_mq) because SCSI's host busy counter
>>> may not be same with counter of blk-mq's inflight tags, especially in case
>>> of none io scheduler.
>>>
>>> So please revert the two commits.
>>
>> Please do, they break changing write cache mode on my SATA drives. You
>> can add my tested-by and/or reported-by to this.
> 
> Jens, how does it break? Could we add a blktest for it?

Yep, it's pretty easy:

# echo "write through" > /sys/block/sde/device/scsi_disk/4:0:0:0/cache_type

and it hangs. For a blktests test, probably check the current value and
ensure we set it to a different value, then restore it.

-- 
Jens Axboe




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