2009/344 Bridging Updates

[Garrett D'Amore]

Okay, with that understanding I think I can give +1 to this project.

There should be guidance somewhere (whitepaper?) that Solaris bridging 
is not expected to be ultra performant.  In other words, you probably 
don't want to use a Solaris host to replace a 10G switch, or with 
multiple aggregated gigabit ports.

    - Garrett

James Carlson wrote:
> Garrett D'Amore writes:
>   
>> James Carlson wrote:
>>     
>>> Fishing for +1s ... has anyone read this?
>>>
>>>   
>>>       
>> I'll reply later today.  I need to check your materials for one thing -- 
>> I'm a bit surprised you intend to disable crossbow polling mode.  The 
>> rest of your proposal (without looking at the detailed changes) looked 
>> good to me.
>>     
>
> This was discussed with Nicolas Droux and Venugopal Iyer at length.
> The issue is that the hooks I have in the mac layer in order to
> intercept packets at a low level for bridging purposes are in a place
> where only interrupt-based packets are processed.
>
> I investigated adding hooks for the polled mode, and got a handle on
> what might be required, but the Crossbow folks suggested that I just
> disable polling for these ports.  The reasons are several:
>
>   - The data paths used for polling mode are diverse, complicated, and
>     very performance sensitive.  Adding hooks there would likely lower
>     performance for the most critical high-end features, and would be
>     complex as many of the functions involved have doppelgaengers.
>
>   - Polling mode is used only for high-speed high-performance
>     interfaces, and enabling bridging forces us turn on promiscuous
>     mode (as a basic requirement of doing bridging), which in turn
>     substantially impacts performance in many ways (not just the extra
>     data, but also by causing performance features to be disabled as a
>     side-effect).  In other words, there's a fundamental conflict
>     between these two goals: if you want to sling packets fast, you
>     don't want bridging, and if you want bridging, you have to be
>     willing to give up the upper end (>1Gbps) of performance.
>
>   - The whole issue goes away when the Crossbow team redesigns the
>     classifier components so that they're able to handle the
>     functionality required for bridging.  (We don't currently have an
>     ETA on that, though it's not expected to be immanent, which is why
>     the bridging project is going forward with the existing design.)
>
>