Re: [Xen-devel] [PATCH RFC 0/3] Move RTC interrupt injection back into the vpt code.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.02.14 at 12:52, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:
> On Thu, Feb 13, 2014 at 5:39 PM, Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx> wrote:
>> On 13/02/14 17:32, Tim Deegan wrote:
>>> Hi,
>>>
>>> This series implements the most recent idea I was proposing about
>>> reworking the RTC PF interrupt injection.
>>>
>>> Patch 1 switches handling the !PIE case to calculate the right answer
>>> for REG_C.PF on demand rather than running the timers.
>>> Patch 2 switches back to the old model of having the vpt code control
>>> the timer interrupt injection; this is the fix for the w2k3 hang.
>>> Patch 3 is just a minor cleanup, and not particularly necessary.
>>>
>>> N.B. In its current state it DOES NOT WORK.  I got distracted by
>>> other things today and didn't get a chance to finish working on it,
>>> but I wanted to send it out for feedback on the general approach.
>>> If it seems broadly acceptable then either I can pick it up again next
>>> week or maybe Andrew can look at fixing it.
>>>
>>> Cheers,
>>>
>>> Tim.
>>>
>>
>> I should have time to look at the series tomorrow.
> 
> The next question to ask is this:
> 
> This is the last big disruptive bug / bugfix on my list.  We're
> planning on cutting an RC Monday probably, with a test day Tuesday.
> This bug was originally marked as "Not for 4.4".
> 
> So our options are:
> * Delay the release, waiting for this new series to be ready
> * Take the patch Andy posted last week for now, and backport Tim's fix
> when it's ready
> * Release without this bug being fixed
> 
> As a reminder (for those who haven't been following the thread), the
> effect of this bug is that w2k3 guests sometimes hang during boot.
> I'm not sure exactly how often this is, but from talking to Andy it
> seems to be fairly low -- one percent maybe?  The code is very subtle
> and any change may risk causing similar hangs in other situations; in
> particular we would want to be able to test it pretty well.
> 
> At the moment I'm leaning towards not delaying the release for it.
> That could either mean checking the patch we have to hand today (so it
> can make it into the RC Monday hopefully), or just going without it.

I thought we already agreed that Andrew's patch as-is is not an
option. And with the same code being in 4.3, leaving this issue
un-fixed if no sufficiently tested patch becomes ready in time seems
like the better option. Once we have a fix, and it got some extended
exposure in -unstable, we could then still backport it to both 4.4.x
and 4.3.x.

Jan


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