On 11/12/21 8:19 AM, Jessica Clarke wrote:
On 11 Nov 2021, at 11:31, Randall Stewart <r...@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 <r...@freebsd.org>
AuthorDate: 2021-11-11 11:28:18 +0000
Commit: Randall Stewart <r...@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.
We discussed this a bit on IRC, but I think in this case the default CC_*
options belong in DEFAULTS like the default GEOM_PART_* options rather
than in GENERIC. (Though we mostly avoid changing DEFAULTS, this is one
of the rare cases when I think it makes sense.) Handling the default for
CC_DEFAULT does not work in DEFAULTS since you can't later override it,
but that could be handled by simply having the default for CC_DEFAULT live
in the code itself under an #ifndef instead.
I think Warner is already testing a patchset to make this change.
--
John Baldwin
