Re: [PATCH 2/2] libata: turn off NCQ if queue depth is adjusted to 1

[Tejun Heo <htejun@gmail.com>]

Ric Wheeler wrote:
> Jens Axboe wrote:
>> On Sat, Sep 30 2006, Alan Cox wrote:
>>> Ar Sad, 2006-09-30 am 20:04 +0200, ysgrifennodd Jens Axboe:
>>>> On Sat, Sep 30 2006, Tejun Heo wrote:
>>>>     
>>>>> Turn off NCQ if queue depth is adjusted to 1.
>>>>>       
>>>> I had thought of that too but discarded it - it would be nicer to have
>>>> an independent way of turning off NCQ. Say you are debugging a weird 
>>>> FIS
>>>> issue, NCQ depth 1 is still a different beast to non-NCQ. I see Jeff
>>>> already applied the patches, but just thought I'd voice my opinion.

Yeah, I was putting off this patch for the same reason.  0 depth would 
have been nice but SCSI midlayer filters such input and libata still 
doesn't have its own sysfs tree.  So, this was the middle ground.

>>> I've got a blacklist for NCQ in my work tree but really we need the
>>> vendors to help fill it. So far it has some raptors in it but I am sure
>>> there are more, and I am sure there are cases we should be advising
>>> newer firmware or just tweaking our queue sizes etc.
>>
>> Lots of the older Maxtors are pretty crappy for NCQ, so those too. Queue
>> size tweaks fixed them for me (as low as 4, and I can't say for sure if
>> it fixes all crashes).

I'm gonna update EH such that NCQ is turned off after certain number of 
errors.  That should at least eventually make the machine usable in such 
cases, but we definitely need NCQ blacklist.

> We have to be careful with the blacklisting - specifically, drive model 
> is often less critical than the version of the firmware (which gets 
> updated as people work drives through qualification, etc).
> Updating drive firmware for end users is pretty rare (and almost all 
> tools are still DOS based ;-)).
> 
> Certain drives should default to non-NCQ (based on model), but we should 
> be able to enable it if the firmware supports it.
> 
> Most of the newest drives are fine, but we will still need something 
> like Tejun's fix to be able to turn it off for the odd cases that show 
> up in certain odd applications, etc.

Ric, can you press harddisk vendors hard enough such that those model 
and revision numbers squeeze out of them?

Thanks.

-- 
tejun