[lustre-devel] Should we have fewer releases?

Christopher J. Morrone morrone2 at llnl.gov
Thu Nov 5 13:45:02 PST 2015


Hi,

I think that Cory meant to send his message to this list.  Please read 
his comment at the end before reading my reply here.

Peter Jones is summarized in those notes as saying that how long 
releases take seems to depend on how much change was introduce into the 
tree.  I agree; this is a causal relationship.

I believe that if our six months releases are often late and take in the 
7-9 month range, then I think that planned nine month releases will in 
actuality take 12+ months.

It may not be the current advocate's reason for suggesting the longer 
release cycle, but one argument I have heard many times is that a longer 
cycle will reduce the amount of manpower needed to create releases.  I 
don't think that is substantially true.  While there are some fixed 
costs in creating a release, there is no real reason that those fixed 
costs need be a dominant factor for manpower demands.  On the other 
hand, required manpower is almost always going to be strongly 
proportional to, and dominated by, the amount of change we introduce.

If we perform excellent, in-depth reviews on all code changes and we 
also perform strong testing throughout the development cycle, then the 
manpower centered around "release time" need not be very high.  But 
right now our peer reviews aren't quite as in depth as they could be, 
and community testing, while improving of late, is unpredictably applied 
and concentrated near the end of the cycle.  This guarantees a large and 
unpredictable amount of development effort shortly before the release 
date, often resulting in a missed release target.

So lets think about what happens if we extend the development cycle, 
including extending freeze dates.  Assuming only minor, gradual 
improvements in code reviews and continuous testing (a very safe 
assumption, I think), the amount of change introduced into the release 
will be proportionally higher the longer we leave the landing window 
open.  The greater the change, the larger the amount of effort needed to 
stabilize the code after the fact.

Furthermore, I would speculate that extending the release cycle and 
putting off the testing and stabilization effort will actually require a 
super linear increase in the time for that effort.

Consider for instance that the longer we make the release cycle, the 
more likely that bug authors have moved on to another task or project. 
Since this is an open source project we don't have any way to order the 
bug author back to work on her code.  Even if the original author is 
available to work on the bug, she may need significant time to shift 
gears and remember how the code she touched works before she can make 
significant progress.  If the original author is not available, then 
someone else needs to learn that portion of code and that has even more 
obvious impact on time to solution and release.

I think there are also other effects that will conspire (e.g. unexpected 
change interactions) to make the testing and stabilization period grow 
super-linearly with the increase in the landing window.

Therefore, I would argue that lengthening the release cycle will neither 
reduce our manpower needs nor result in more predictable release dates.

On the contrary, we need to go in the opposite direction to achieve 
those goals.  We need to shorten the release cycle and have more 
frequent releases.  I would recommend that we move to to a roughly three 
month release cycle.  Some of the benefits might be:

* Less change and accumulate before the release
* The penalty for missing a release landing window is reduced when 
releases are more often
* Code reviewers have less pressure to land unfinished and/or 
insufficiently reviewed and tested code when the penalty is reduced
* Less change means less to test and fix at release time
* Bug authors are more likely to still remember what they did and 
participate in cleanup.
* Less time before bugs that slip through the cracks appear in a major 
release
* Reduces developer frustration with long freeze windows
* Encourages developers to rally more frequently around the landing 
windows instead of falling into a long period of silence and then trying 
to shove a bunch of code in just before freeze.  (They'll still try to 
ram things in just before freeze, but with more frequent landing windows 
the amount will be smaller and more manageable.)

It was also mentioned in the LWG email that vendors believe that the 
open source releases need to adhere to an advertised schedule.  Having 
shorter release cycles with smaller and more manageable change will 
directly contribute to Lustre releases happening on a more regular schedule.

Those same vendors tend to be concerned that they will not be able to 
productise every single release if they happen on a three month 
schedule.  It is important to recognize that a vendor's product schedule 
need not be directly in sync with every community release.  It is 
actually quite common in the open source world for vendors to select a 
version to productise, and skip over some community releases to find the 
next version which they will productise.  Consider, for instance, the 
Linux kernel.  RedHat selects a version of the kernel to include in RHEL 
and then sticks with the base of code fore many years.  They will 
backport changes as they see fit, but their base on that release remains 
the same.  The next kernel that they decide to package in their product 
will skip over many of the upstream Linux releases.

Some Lustre vendors already operate this way, and the ones that do not 
need to adapt to this common, successful open source model.

Shortening the release cycle will help encourage and sustain an active 
open source community of Lustre developers from a diverse set of 
organizations.

Conversely, lengthening the release cycle will result in less Lustre 
stability and encourage stagnation.  It will make us less nimble, less 
likely to meet the needs of our current user base, and slower to expand 
into new markets.

Lets start working through what process changes we will need to make to 
shorten the development cycles and make lustre releases more often.

Thanks,
Chris

On 11/04/2015 01:16 PM, Cory Spitz wrote:
> Hello, Lustre developers.
>
> On today¹s OpenSFS LWG teleconference call (notes at
> http://wiki.opensfs.org/LWG_Minutes_2015-11-04) I proposed that we change
> the Lustre release cadence from six months to nine months.  Chris M.
> responded (below) that any discussion about development changes should
> happen here on lustre-devel.  I agree, developers need to be on-board.
>
> So what do you think about release changes?  What requirements do you
> have?  What issues would you have if OpenSFS changed the major release
> cadence to nine months?
>
> Thanks,
>
> -Cory
>
> On 11/4/15, 1:58 PM, "lwg on behalf of Christopher J. Morrone"
> <lwg-bounces at lists.opensfs.org on behalf of morrone2 at llnl.gov> wrote:
>
>> On 11/04/2015 10:28 AM, Cory Spitz wrote:
>>
>>> Lustre release cadence
>>> We haven¹t been good about hitting our 6 month schedules
>>> Cory proposed a 9 month cadence just to recognize reality.  Certainly
>>> pros/cons to any scheme.  Should be up for discussion.  How/when to
>>> decide?
>>
>> Any development change like that needs to be discussed on lustre-devel.
>>
>> Chris
>>
>> _______________________________________________
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>> lwg at lists.opensfs.org
>> http://lists.opensfs.org/listinfo.cgi/lwg-opensfs.org
>
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