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Re: [dm-devel] [PATCH 3/5] dm-multipath: remove process_queued_ios()

On 02/03/2014 11:26 AM, Junichi Nomura wrote:
> On 01/31/14 23:55, Hannes Reinecke wrote:
>> Problem here is that pg_init_done() is per path, so at face value
>> SCSI_DH_RETRY is per path, too.
>> So from that we should be retrying this path (and this path only).
>> Hence it would be correct to call queue_delayed_work directly.
>> However, typically any pg_init affects _every_ path in the multipath
>> device (active paths become passive and vice versa).
>> Which seems to be the intended usage, as we're checking for
>> pg_init_in_progress prior to invoking queue_delayed_work().
>> But _if_ we assume that, then we only need to send a _single_
>> pg_init, as this will switch all paths. So again, a call to
>> __pg_init_all_paths will not do the correct thing as it'll
>> send activations to _every_ active path.
> Sending activation for every paths was introduced by this:
>   commit e54f77ddda72781ec1c1696b21aabd6a30cbb7c6
>   Author: Chandra Seetharaman <sekharan us ibm com>
>   Date:   Mon Jun 22 10:12:12 2009 +0100
> So if you make change in the logic, you have to check whether the
> change does not break what the above solved.
>> (And, in fact, we're trying really hard in scsi_dh_rdac
>> and scsi_dh_alua to bunch together all the various pg_init
>> requests precisely for the cited reason).
>> So my inclination here would be to treat SCSI_DH_RETRY
>> as _per path_, and retry only this specific path.
>> IE removing the check to pg_init_in_progress and call
>> queue_delayed_work() directly.
>> IMHO this would impose the least restriction on
>> the internal workings of the various device handlers.
>> What do you think?
> I don't have strong opinion either way. But if we do that, more code
> has to be changed, e.g. the management of retry count.
> Removing the unnecessary workqueue has already a benefit.
> It would be nice to focus on that instead of folding in more changes.
Yes, that's what I've figured, too.
So I've just included the changes you suggested without modifying
the current logic.

I've already sent a new patchset, please check if the changes there
are correct.


Dr. Hannes Reinecke		      zSeries & Storage
hare suse de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)

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