[dm-devel] [PATCH 10/15] libmultipath: change how the checker async is set

[John Stoffel]

>>>>> "Benjamin" == Benjamin Marzinski <bmarzins at redhat.com> writes:

Benjamin> On Mon, Jan 20, 2020 at 03:20:14PM -0500, John Stoffel wrote:
>> >>>>> "Benjamin" == Benjamin Marzinski <bmarzins at redhat.com> writes:
>> 
Benjamin> On Sat, Jan 18, 2020 at 12:43:49PM -0500, John Stoffel wrote:
>> >> >>>>> "Benjamin" == Benjamin Marzinski <bmarzins at redhat.com> writes:
>> >> 
Benjamin> The way that the checkers async mode worked in multipathd didn't make
Benjamin> much sense. When multipathd starts up, all checker classes are in the
Benjamin> sync mode, and any pathinfo() calls on devices would run the checker in
Benjamin> sync mode. However, the First time a checker class was used in
Benjamin> checkerloop, it would set that checker class to async (assuming
Benjamin> force_sync wasn't set).  After that, no matter when a checker from that
Benjamin> class was called, it would always run in async mode.  Multipathd doesn't
Benjamin> need to run checkers in sync mode at all, so don't.
>> >> 
>> >> Sorry, I had a hard time parsing this description, especially the last
>> >> sentence.  Do you mean that checkers should default to async then,
>> >> instead of sync mode?  And from looking at the code, don't you mean
>> >> that you force sync mode?  I guess the question is whether checker
>> >> classes should default sync, or async.  And if they move to async,
>> >> should they stay there?
>> >> 
>> 
Benjamin> Sorry. I mean that right now multipathd runs the checkers from pathinfo(),
Benjamin> wait_for_pending_paths() and check_path(). When multipathd starts, all
Benjamin> checkers are in sync mode. The first time a checker is run from
Benjamin> check_path(), it is switched to async mode, and stays there for the rest
Benjamin> of the time multipathd is runing.
>> 
Benjamin> There is no need for multipathd to run checkers in sync mode at all, so
Benjamin> we shouldn't be doing so for these first checks.
>> 
>> Thanks, that makes the entire issue much more clear.  This raises the
>> question of why there is a sync mode at all then?  In any case, the
>> above makes the issue more understandable.

Benjamin> The multipath command, which uses the same checkers, runs in sync mode.

Crystal clean now.  Thanks for your patience!