flowtable usable or not (was: Re: [CFT] modular kernel config

Florian Smeets flo at FreeBSD.org
Tue Feb 28 23:08:18 UTC 2012

On 28.02.12 23:14, Doug Barton wrote:
> On 2/28/2012 10:48 AM, Arnaud Lacombe wrote:
>> You will sure go really far with this kind of "It is broken ? Let's
>> not fix it and disable it instead" mentality, even more when coming
>> from a committer.
>> As long as there will be these kind of comments around here, FreeBSD
>> will deserve nothing but to keep dying piece by piece, and it will be
>> deserved.
> In general, I tend to agree with you, but in this case it's useful to
> know the history of the flowtable option.
> 1. It was introduced in -current
> 2. It received fairly good testing, was pronounced good and useful, and
> MFC'ed.
> 3. Several releases happened with flowtable.
> 4. Users started to report problems that were ultimately tracked down to
> flowtable.
> 5. Ultimately it was decided that flowtable was not a universal good.
> 6. The developer of the option agreed that it should be disabled by
> default until such time as it can be fixed.
> 7. The fixing hasn't happened yet.

I talked to Kip Macy, who implemented flowtable, about this. He thinks
that the problem was caused by inappropriate default setting of
net.inet.ip.output_flowtable_size. This should have been fixed by
r205488 which was MFC'd to 8 and should be part of 8.2 and of course
9.0. However nobody who experienced the problem wanted to try any of
these releases with flowtable enabled, so we still don't know if it's
fixed or not.

Should anyone try this it could certainly be the case that
net.inet.ip.output_flowtable_size needs to be tuned even more.


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