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

[Benjamin Marzinski]

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.

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

-Ben

> 
> John