netdev - Re: Keep bpf-next always open

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Message-ID: <20200923222812.oxhp6zznwdnkiffs@ast-mbp.dhcp.thefacebook.com>
Date:   Wed, 23 Sep 2020 15:28:12 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...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 Wed, Sep 23, 2020 at 10:23:51PM +0000, Song Liu wrote:
> 
> 
> > 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? 

It will create headaches for linux-next that merges bpf-next/master.
All linux-next trees should not add patches to those trees that are not going
into the merge window.