Re: [PATCH 02/24] workqueue: defer work to a draining queue

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On Mon, Dec 19, 2011 at 2:08 PM, Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hello,
>
> On Mon, Dec 19, 2011 at 02:01:47PM -0800, Dan Williams wrote:
>> > Dan, as I replied before, I'm not a big fan of this approach.
>>
>> Sorry I must have missed it, I can't seem to find a reply in the archives?
>
> Yeah, I can't find it either.  I definitely remember writing it.
> Hmmm... weird.  Either I'm finally losing my mind or it didn't get out
> for some reason.  Sorry. :)

As long as it's you losing your mind and not me :-).

>> > For
>> > now, I think it would be best to add private wrapper in libsas to
>> > support deferring unchained work items while draining.
>>
>> Ok, a form of this was nak'd by James before [1], but I can try again
>> with pushing this chained submission checking down into scsi.
>
> The issues I see with the proposed change is,
>
> * There doesn't seem to be high demand for it.
>
> * It isn't implemented the right way - it introduces unnecessary and
>  hidden ordering between chained work items being drained and newly
>  queued unchained ones.  We can try to do it properly without
>  affecting new unchained work items but I'm not sure the added
>  complexity is justified given the first issue.

Fair enough.

> I don't think adding a wrapper which defers queueing while draining is
> going on would be too complex, right?

No, I think it should be pretty straightforward to teach libsas not to
throw anything else at the queue while a drain is pending.

Thanks,
Dan
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