netdev - Re: Keep bpf-next always open

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Message-ID: <7DAA1D76-860C-4058-9D5F-7A87DB45B8C8@fb.com>
Date:   Wed, 23 Sep 2020 22:23:51 +0000
From:   Song Liu <songliubraving@...com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: Keep bpf-next always open



> On Sep 23, 2020, at 3:14 PM, Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> 
> On Wed, Sep 23, 2020 at 02:48:24PM -0700, Andrii Nakryiko wrote:
>> On Wed, Sep 23, 2020 at 2:20 PM Alexei Starovoitov
>> <alexei.starovoitov@...il.com> wrote:
>>> 
>>> BPF developers,
>>> 
>>> The merge window is 1.5 weeks away or 2.5 weeks if rc8 happens. In the past we
>>> observed a rush of patches to get in before bpf-next closes for the duration of
>>> the merge window. Then there is a flood of patches right after bpf-next
>>> reopens. Both periods create unnecessary tension for developers and maintainers.
>>> In order to mitigate these issues we're planning to keep bpf-next open
>>> during upcoming merge window and if this experiment works out we will keep
>>> doing it in the future. The problem that bpf-next cannot be fully open, since
>>> during the merge window lots of trees get pulled by Linus with inevitable bugs
>>> and conflicts. The merge window is the time to fix bugs that got exposed
>>> because of merges and because more people test torvalds/linux.git than
>>> bpf/bpf-next.git.
>>> 
>>> Hence starting roughly one week before the merge window few risky patches will
>>> be applied to the 'next' branch in the bpf-next tree instead of
>> 
>> Riskiness would be up to maintainers to determine or should we mark
>> patches with a different tag (bpf-next-next?) explicitly?
> 
> "Risky" in a sense of needing a revert. The bpf tree and two plus -rc1 to -rc7
> weeks should be enough to address any issues except the most fundamental ones.
> Something like the recent bpf_tail_call support in subprograms I would consider
> for the "next" branch if it was posted a day before the merge window.
> In practice, I suspect, such cases will be rare.
> 
> I think bpf-next-next tag should not be used. All features are for [bpf-next].
> Fixes are for [bpf]. The bpf-next/next is a temporary parking place for patches
> while the merge window is ongoing.

I wonder whether we can move/rename the branch around so that the developers can 
always base their work on bpf-next/master. Something like:

Long before merge window for 5.15:	
We only have bpf-next/master

1 week before merge window for 5.15:	
Clone bpf-next/master as bpf-next/for-5.15

>From -1 week to the end of merge window
Risky features only goes to bpf-next/master, bug fix goes in both master and for-5.15

After merge window:
Fast forward bpf-next/master based on net-next. Deprecate for-5.15.

Would this work? 

Thanks,
Song