Re: IFQ_ENQUEUE argument refactor (was Re: RFC: ALTQ caller refactor)

[Thor Lancelot Simon <tls%panix.com@localhost>]

On Mon, Apr 04, 2016 at 05:25:14PM +0900, Kengo NAKAHARA wrote:
> 
> You are right. Hmm..., I'm sorry, I change my objective. I think it could
> be better to use pool cache for m_tag itself.

The tags are a mess and I've seen them seriously impact performance in
numerous profiles of the network stack.  In fact, at a former employer,
it was sort of an expected thing: each time we'd experiment with some
new feature of the stack (vlan tagging, altq, etc.) we'd see a
performance degradation which profiling would revel traced back to the
allocation, use, and deallocation of mbuf tags.

I would suggest that the only "proper" use of mbuf tags as currently
implemented is experimentation.  Uses of the tags which have been in
the tree for a decade or more should be subsumed into the mbuf
datastructure itself, with some care taken to not make it too large,
or perhaps a single, "standard" extension structure could be defined
to capture the less-common cases.

Thor