[Xen-devel] RFC: Criteria for checking in core scheduling series

[George Dunlap <george.dunlap@xxxxxxxxxx>]

There was a discussion on the community call about the core scheduling
series being developed by Juergen Gross [1].  The conclusion can be
summarized as follows:

* We normally wait to check in series until they are quite good -- all
the i's dotted and all the t's crossed

* This is for several reasons; primarily because once code gets checked
in, it rarely gets looked at again.  In particular, there's nothing
stopping the submitter from neglecting to do important clean-ups, in
spite of their best intentions; leaving the maintainer or the rest of
the community to do it.

* However, for particularly long, complicated series like the core
scheduling series, this can have significant downsides.  Rebasing a
60-patch branch regularly is a lot of churn for little value; and core
parts of the series which are mostly complete are currently only getting
sporadic dev testing rather than the wide range of testing they would
get from being in staging.

* XenServer and SuSE are both long-term community members with a strong
incentive to maintain and improve the feature; so the risk of the
feature being left for the community to maintian is relatively now.

With all those things in mind, the conclusion was to lower the
"check-in" threshold from what it normally is, in order to allow the
series to be checked in in the near future, in enough time at least for
the "default off" to be well-tested by the 4.13 release.

The criteria we sketched out were:

* All the patches still need appropriate Ack / R-b's

* There should be reason to believe that the series will have little to
no impact on "thread mode" (threads being the unit of scheduling; i.e.,
the status quo)

WRT the second point, apparently XenServer have been testing the series
regularly for some time, and are satisfied from a testing perspective
that there is no significant degradation for the series when in "thread
mode".

So this would really be a recommendation / license to the various
maintainers involved; primarily Dario, I think (since I probably won't
have time to review the series).

No decisions are official until discussed on xen-devel; so the decision
will not be considered official until a few days have passed without
objection.  And of course, if anyone at the meeting had a different
understanding of what was said, or has something to add, please do so.

Thanks,
 -George

[1] https://patchew.org/Xen/20190809145833.1020-1-jgross@xxxxxxxx/

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