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Re: [dm-devel] [PATCH 4/6] dm-multipath: remove process_queued_ios()



On 02/03/14 21:18, Hannes Reinecke wrote:
> On 02/03/2014 01:08 PM, Junichi Nomura wrote:
>> On 02/03/14 17:18, Hannes Reinecke wrote:
>>> We only need to take care to add a small delay when calling
>>> __pg_init_all_paths() to move processing off to a workqueue;
>>> pg_init_done() is run from an interrupt context and needs to
>>> complete as fast as possible.
>> ...
>>> @@ -1217,9 +1185,11 @@ static void pg_init_done(void *data, int errors)
>>>  
>>>  	if (!m->pg_init_required)
>>>  		m->queue_io = 0;
>>> -
>>> -	m->pg_init_delay_retry = delay_retry;
>>> -	queue_work(kmultipathd, &m->process_queued_ios);
>>> +	else {
>>> +		m->pg_init_delay_retry = delay_retry;
>>> +		__pg_init_all_paths(m, 50/HZ);
>>> +		goto out;
>>> +	}
>>>  
>>
>> I forgot to comment on this.
>> Adding delay to queue_work() doesn't make it fast.
>> So I couldn't see why this "50/HZ" delay has to be added
>> and where this value comes.
>>
> Well, it wasn't probably the best choice of words.
> 
> Thing is, without a delay the workqueue item will be executed
> directly (cf __queue_delayed_work()).
> But pg_init_done() is run from an interrupt context, and as such any
> memory allocations have to be atomic.
> So if we were to call queue_delayed_work() without any delay
> we will end up calling scsi_dh_activate from an interrupt context,
> too, but there we most definitely do _not_ have only atomic allocations.
> Hence the delay.

Work is executed in the worker context (in this case by kmpath_handlerd).
Isn't it?

-- 
Jun'ichi Nomura, NEC Corporation


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