Re: [PATCH] Re: SYNCHRONIZE_CACHE from sd_preppare_flush does not have retries.!

[Mike Christie <michaelc@cs.wisc.edu>]

On 04/20/2010 09:54 AM, Bernd Schubert wrote:
> On Tuesday 20 April 2010, Desai, Kashyap wrote:
>>>>>> all block device flushes or is this more device specific? I was
>>>>>> thinking that we may want to create a sysfs interface under the
>>>
>>> block
>>>
>>>>>> dirs and have blk-sysfs.c and blk-barrier.c handle this.
>>>
>>> queue_flush
>>>
>>>>>> could set the timeout and retries that is set by some new files
>>>
>>> under
>>>
>>>>>> /sys/block/sdX/queue/ ?
>>
>> Thanks a lot for your comments.
>>
>> This is very close to my understanding. I feel this is more close to block
>>   layer and I am almost agreeing with your thought. I tried to understand
>>   why upstream does not have retries at queue_flush()/sd_prepare_flush() ???
>>   It looks like there is not specific reason. If I am wrong can someone
>>   explain is there any specific reason not to set rq->retries in
>>   sd_prepare_flush?
>
> I don't understand why we should need another queue timeout, when we
> already have a device timeout that is used as queue timeout?


I think a possible problem is that the one timeout setting is now being 
used for two different operations. Currently, for disks that timeout is 
used for READ/WRITEs. For the sync cache, if we are hitting a problem 
with it taking longer than the current value of 30 secs, then could we 
want to set the READ/WRITE timeout to a lower value like 60 secs, but 
then the sync cache timeout might have to be multiple minutes.