Re: git: b8d60729deef - main - tcp: Congestion control cleanup.

From: Jessica Clarke <jrtc27_at_freebsd.org>
Date: Fri, 12 Nov 2021 16:19:04 UTC
On 11 Nov 2021, at 11:31, Randall Stewart <rrs@FreeBSD.org> wrote:
> 
> The branch main has been updated by rrs:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=b8d60729deefa0bd13e6a395fcab4928e6e10445
> 
> commit b8d60729deefa0bd13e6a395fcab4928e6e10445
> Author:     Randall Stewart <rrs@FreeBSD.org>
> AuthorDate: 2021-11-11 11:28:18 +0000
> Commit:     Randall Stewart <rrs@FreeBSD.org>
> CommitDate: 2021-11-11 11:28:18 +0000
> 
>    tcp: Congestion control cleanup.
> 
>    NOTE: HEADS UP read the note below if your kernel config is not including GENERIC!!
> 
>    This patch does a bit of cleanup on TCP congestion control modules. There were some rather
>    interesting surprises that one could get i.e. where you use a socket option to change
>    from one CC (say cc_cubic) to another CC (say cc_vegas) and you could in theory get
>    a memory failure and end up on cc_newreno. This is not what one would expect. The
>    new code fixes this by requiring a cc_data_sz() function so we can malloc with M_WAITOK
>    and pass in to the init function preallocated memory. The CC init is expected in this
>    case *not* to fail but if it does and a module does break the
>    "no fail with memory given" contract we do fall back to the CC that was in place at the time.
> 
>    This also fixes up a set of common newreno utilities that can be shared amongst other
>    CC modules instead of the other CC modules reaching into newreno and executing
>    what they think is a "common and understood" function. Lets put these functions in
>    cc.c and that way we have a common place that is easily findable by future developers or
>    bug fixers. This also allows newreno to evolve and grow support for its features i.e. ABE
>    and HYSTART++ without having to dance through hoops for other CC modules, instead
>    both newreno and the other modules just call into the common functions if they desire
>    that behavior or roll there own if that makes more sense.
> 
>    Note: This commit changes the kernel configuration!! If you are not using GENERIC in
>    some form you must add a CC module option (one of CC_NEWRENO, CC_VEGAS, CC_CUBIC,
>    CC_CDG, CC_CHD, CC_DCTCP, CC_HTCP, CC_HD). You can have more than one defined
>    as well if you desire. Note that if you create a kernel configuration that does not
>    define a congestion control module and includes INET or INET6 the kernel compile will
>    break. Also you need to define a default, generic adds 'options CC_DEFAULT=\"newreno\"
>    but you can specify any string that represents the name of the CC module (same names
>    that show up in the CC module list under net.inet.tcp.cc). If you fail to add the
>    options CC_DEFAULT in your kernel configuration the kernel build will also break.

Not doing so breaks tinderbox, as well as configs not hooks up to
tinderbox. I don’t think this is acceptable.

Jess