Friday, January 25, 2008

Clearview/UV putback

Folks watching Nevada putbacks will have noticed at least 3 flag days in the past 24 hours. I want to take a second to talk about the first of them. (I'll talk about the second in a follow up post.)

The first, Clearview/UV, is about providing GLDv3-like features to legacy NIC drivers, and about providing friendlier names to device drivers. I will confess that I've not had a chance to play with any of these features yet, but I think that they are likely to be one of the more important putbacks to OpenSolaris this year. This putback fundamentally changes network administration by offering the ability to use "logical naming" for network device drivers.

The other important thing here is that some folks may believe that the Nemo Unification offered by Clearview/UV means that those legacy drivers don't need to be converted. This is not true. Conversion to GLDv3 still offers significant and tangible benefits to network device drivers:
  1. Performance. The translation layer that Clearview provides adds a performance hit for legacy drivers. Its also the case that legacy NIC drivers are unable to benefit from several of the performance benefits that GLDv3 offered (direct function calls, mblk chaining, etc.)
  2. Full VLAN support. Legacy drivers that don't support the undocumented VLAN features aren't able to offer full size VLAN frames. VLANs still work, but you have to shrink your MTU by 4 bytes.
  3. Certain upcoming GLDv3/Crossbow features. Legacy drivers won't be able to take advantage of upcoming features in GLDv3 from Crossbow. These include various interrupt mitigation techniques and multiple hardware ring support.
The upshot is that the Nemo Unification represents a band-aid for legacy NIC drivers. If you own the code for one or more of these, you really should still have a plan for GLDv3 conversion, unless your willing to accept that your driver is a second class citizen in OpenSolaris. (Note that GLDv3 is still Consolidation Private. Figuring out that Corollary to that fact is left as an exercise to the readers.)

Folks that want help with such a conversion should contact me.

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