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Re: [Xen-devel] Upcoming RC0

At 15:21 +0100 on 03 May (1367594473), George Dunlap wrote:
> IanC suggested that we should have a short code-freeze window before
> each RC to make sure that nothing is introduced that will cause test
> failures.  So I'm asking committers to hold off on committing anything
> that is not directly related to making the tests pass, or to fixing
> specific issues that need to be fixed before RC0.


> The one major bug we have outstanding is the RTC one -- as that
> basically prevents w2k3 from working at all, it would be good to have
> that one fixed if possible by the test day on Wednesday.
> Keir, IanC, IanJ, do you guys have any opinions on this one?
> Jan thinks that since we have an understanding of what the issue is,
> and a patch series that fixes the problem (as far as we can tell) for
> w2k3.
> Tim things we just don't have enough time to be sure we can catch all
> the bugs, so we should revert all the RTC made in the last few months.

Well, mainly the one change that scares me is the switch from having vpt
inject the interrupts to having RTC code (conditionally) inject them.
Unfortunately, given the amount of fixes that have followed that code,
it's not as simple as a plain revert of a single patch.  And I have _no_
time between now and Tuesday to disentangle that one change with any
confidence of doing it right.

So with the release so close, I think it might be as well to revert all
the RTC changes since 4.2.  That includes reverting a few genuine fixes
(but AIUI nothing that's been seen in the field) to get to a known good
state.  Then we apply 'em all again as soon as we branch[1].

The other option is to take the rest of Jan's current series, which
keeps all the code changes but disables the end result.  IMHO, this
needs someone to commit to serious testing, esp. of all the old crusty
OSes that are likely to rely on the RTC's behaviour.  And at the end we
don't get the main benefit (avoiding pointless timer interrupts) either


[1] When are we branching, btw?  At rc0 or later?

> I can see the point of both sides; however, Tim found some issues even
> in the patch series that Jan posted recently, which (sorry to be
> frank, Jan) doesn't give me confidence that we won't have random bugs
> that we end up tripping over after the release.
> Overall I'd rather defer to Tim, Jan, and Keir; but if I were asked to
> make a recommendation, I would go with Tim's.
> As long, that is, as we are confident that we can back the changes out
> easily.  If reverting the changes is a complicated business, we risk
> bugs either way; in which case we might as well move forward.
>  -George

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