Re: [GIT PULL] KVM updates for the 3.4 merge window

[Avi Kivity <avi@redhat.com>]

On 03/26/2012 06:21 PM, Ingo Molnar wrote:
> * Avi Kivity <avi@redhat.com> wrote:
>
> > Say a fix comes in which needs to be mainlined during -rc.  So 
> > I put it in some other branch, to be sent off to Linus in a 
> > few days after maturing a little.  Meanwhile developers see an 
> > incomplete tree, since that patch is not in it.
> > 
> > Once Linus pulls, I can merge it back (or even before, if I'm 
> > reasonably certain it's not going to change), but it leaves a 
> > history of unneeded merges.  Or we can do throwaway merges 
> > like tip.git.
>
> We don't do throwaway merges in the -tip development branches 
> themselves, i.e. in tip:sched/core, tip:perf/core, 
> tip:timers/core, etc.
>
> When a fix goes into tip:sched/urgent then until Linus merges it 
> it's not in tip:sched/core. 99% of the fixes don't *have to* go 
> into sched/core straight away.
>
> In the odd case where there's some dependency, we can manually 
> merge it into tip:sched/core ahead of Linus pulling into an -rc. 
> Those rare merges are not a problem, and I explain the reason in 
> the merge commit itself.
>
> If you look at:
>
>  gll v3.2..v3.3 | grep -E '/urgent.*/core'
>
> you'll see that I only had to do it once in the previous cycle:
>
>  d6c1c49de577 Merge branch 'perf/urgent' into perf/core
>
> and the changelog explains the background:
>
> Merge reason: Add these cherry-picked commits so that future changes
>               on perf/core don't conflict.
>
> it was a rare, oddball situation where we cherry-picked 
> perf/core changes into perf/urgent. Extra merges are perfectly 
> fine in that case.
>
> The 'throwaway' tip:master branch you are probably referring to 
> is basically just a testing branch, a convenient merged tree of 
> the one dozen maintainer trees that are hosted in -tip. Since we 
> don't want to force Linus's hand of him being able to reject 
> individual trees we don't merge them properly - hence the 
> integrated tree is a throwaway tree in theory.
>
> In practice I tend to throw it away only once per cycle, around 
> -rc1, once all pending trees went to Linus. tip:master is not 
> used for any Git based contribution work - it's for testing, 
> it's for people who want to work with patches - the commits 
> themselves always go into persistent non-rebasing, append-only 
> Git trees.
>
> If we mess up bisectability we do a delta fix. When choosing 
> between somewhat better bisectability and a proper history that 
> others can rely on then proper history wins hands down.
>

Okay, we'll adopt a similar workflow for the future.

-- 
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