[PATCH] Add a new TCP_IGNOREIDLE socket option

[Sepherosa Ziehau]

On Wed, Feb 20, 2013 at 11:59 AM, Lawrence Stewart <lstewart at freebsd.org> wrote:
> Hi Sephe,
>
> On 02/20/13 13:37, Sepherosa Ziehau wrote:
>> On Wed, Feb 20, 2013 at 9:46 AM, Lawrence Stewart <lstewart at room52.net> wrote:
>>> *crickets chirping*
>>>
>>> Time to move this discussion forward...
>>>
>>>
>>> If any robust counter-arguments exist, now is the time for us to hear
>>> them. I haven't read anything thus far which convinces me that we should
>>> not provide knobs to tune our stack's dynamics.
>>>
>>> In the absence of any compelling counter-arguments, I would like to
>>> propose the following:
>>>
>>> - We rename the net.inet.tcp.experimental sysctl node introduced in
>>> r242266 for IW10 support to net.inet.tcp.nonstandard, and re-parent the
>>> initcwnd10 sysctl under this node.
>
> I should also add that I think initcwnd10 should be changed to initcwnd
> and take the number of segments as a value.

Yeah, I would suggest the same.

>
>>> - We introduce a new net.inet.tcp.nonstandard.allowed sysctl variable
>>> and default it to 0. Only when it is changed to 1 will we allow starkly
>>> non standards compliant behaviour to be enabled in the stack. As a more
>>> complex but expressive alternative, we can make the sysctl take a bit
>>> mask or CSV string which specifies which non-standard options the sys
>>> admin permits (I'd prefer this as we can easily test non-standard
>>> options like IW10 in head without blanket enabling all non standard
>>> behaviour).
>
> To be clear, my proposal is that specifying an allowed option in
> net.inet.tcp.nonstandard.allowed would not enable it as the default on
> all connections, but would allow the per-application mechanism we define
> to set the option. Setting net.inet.tcp.nonstandard.option_x to 1 would
> enable the option as default for all connections.
>
>>> - We introduce a new net.inet.tcp.nonstandard.noidlereset sysctl
>>> variable, and use it to enable/disable window-reset-after-idle behaviour
>>> as proposed by John.
>>>
>>> - We don't introduce a TF_IGNOREIDLE sockopt, and instead introduce a
>>> more generic sockopt and/or mechanism for per-application tuning of all
>>> options which affect stack dynamics (both standard and non-standard
>>> options). I'm open to suggestions on what this could/should look like.
>>
>> Lawrence,
>>
>> A route metric?  BTW, as for IW10, it could also become a route metric
>> (as proposed by the draft author's presentation
>> http://www.ietf.org/proceedings/79/slides/tcpm-0.pdf)
>
> Are you suggesting having the ability to set knobs as route metrics in
> addition to sysctl and a per-app mechanism? If so then I am very much in
> favour of this. Assuming an option has been allowed in
> net.inet.tcp.nonstandard.allowed, it should be able to be set by an
> application or on a route, perhaps with a precedence hierarchy of app
> request trumps route metric trumps system default setting?

I suggest using route metrics in addition to the global sysctls; route
metrics take precedence over global sysctls.  I don't object the
per-socket settings though.  However, IMHO, these options (IW10 and
ignoring idle restart, and probably others) are administrative, so
applications probably should not mess with them.

Best Regards,
sephe

-- 
Tomorrow Will Never Die