Re: [PATCH v6] mmc: support BKOPS feature for eMMC

[Adrian Hunter <adrian.hunter@intel.com>]

On 20/01/12 09:50, Jaehoon Chung wrote:
> On 01/20/2012 04:31 PM, Adrian Hunter wrote:
> 
>> On 19/01/12 17:32, S, Venkatraman wrote:
>>> On Thu, Jan 19, 2012 at 5:14 PM, Adrian Hunter <adrian.hunter@intel.com> wrote:
>>>> On 19/01/12 13:33, Jaehoon Chung wrote:
>>>>> Hi Adrian.
>>>>>
>>>>> On 01/19/2012 07:21 PM, Adrian Hunter wrote:
>>>>>
>>>>>> On 19/01/12 07:29, Jaehoon Chung wrote:
>>>>>>> Enable eMMC background operations (BKOPS) feature.
>>>>>>>
>>>>>>> If URGENT_BKOPS is set after a response, note that BKOPS
>>>>>>> are required. After all I/O requests are finished, run
>>>>>>> BKOPS if required. Should read/write operations be requested
>>>>>>> during BKOPS, first issue HPI to interrupt the ongoing BKOPS
>>>>>>> and then service the request.
>>>>>>
>>>>>> This still does not seem to address my earlier comment which was:
>>>>>>
>>>>>> The main problem with bkops is:
>>>>>>
>>>>>>      If the status is at level 3 ("critical"), some operations
>>>>>>      may extend beyond their original timeouts due to maintenance
>>>>>>      operations which cannot be delayed anymore.
>>>>>>
>>>>>> This means:
>>>>>>
>>>>>>      1. at level 3 either bkops are run or the timeout of the next
>>>>>>      (data?) operation is extended
>>>>>>
>>>>>>      2. at level 3 either the bkops must not be interrupted or the
>>>>>>      level must be rechecked after interruption and bkops run again
>>>>>>      if the level is still 3, or the timeout of the next (data?)
>>>>>>      operation is extended
>>>>>>
>>>>>
>>>>> This patch didn't issue the HPI when bkops-status is level2-3
>>>>> (URGENT_BKOPS case).
>>>>> I didn't understand that must be recheck?? it's case of using HPI..?
>>>>> If HPI didn't issue,though must be recheck bkops status?
>>>>> And level-1 control should be considered for future-work.
>>>>> I will also modify the patch comment..it's confused something.
>>>>
>>>> 1. Say there are 2 write requests queued and after the first write request
>>>> the bkops level is 3.  That means the 2nd write request may timeout because
>>>> the normal timeout rules do not apply.
>>>>
>>>> Thus:
>>>>        1. at level 3 either bkops are run or the timeout of the next
>>>>        (data?) operation is extended
>>>>
>>>> 2. Say you are running bkops because the level was 3 and a write request
>>>> arrives.  You use HPI to interrupt the bkops, but the bkops level may still
>>>> be 3, so the write request may timeout.  Hence:
>>>>
>>>>        2. at level 3 either the bkops must not be interrupted or the
>>>>        level must be rechecked after interruption and bkops run again
>>>>        if the level is still 3, or the timeout of the next (data?)
>>>>        operation is extended
>>>>
>>>
>>> A naive question perhaps, but don't the current timeout values include
>>> sufficient
>>> buffer to do implicit garbage collection anyways ?
>>
>> Maybe, but the problem is the JEDEC specification says otherwise.  This bit
>> is a quote:
>>
>> 	If the status is at level 3 ("critical"), some operations
>> 	may extend beyond their original timeouts due to maintenance
>> 	operations which cannot be delayed anymore.
>>
>> I think level 3 is a very rare case so I would just run bkops and wait for
>> it to finish without interruption.
> 
> Yes..JEDEC spec say those..but I think not bad that wait for bkops-done..
> actually i didn't know how long time run the bkops...
> so i think the use the hpi command..then re-check the bkops-status until clear status.
> (i think the request's priority is higher than any bkops status)

Not if the request is going to fail with a timeout error because bkops is at
level 3.

> 
> it would be open to interpretation that sentence.
> 
> Best Regards,
> Jaehoon Chung
> 
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> 
> 
>