mbuf revision, testers/comments wanted.
jroberson at jroberson.net
Sat Jan 31 15:20:23 PST 2009
I have been experimenting with different revisions to the mbuf api to
improve performance and simplify code. This patch is the first of several
proposed steps towards those goals. The aim of this patch is two fold;
1) Revising the reference counting system so that we can eliminate
reference uma zones and the significant uma_find_refcnt() costs in some
workloads. This is done by making all mbufs reference counted and using
the owning mbuf's ref for the ext_ref. In this model we never reference
data, we only reference other mbufs owning the data.
2) Improve allocation and free performance by reducing the special cases
in the format and using inlines when appropriate. In particular, the
simplification of the m_ext structure yields less code and confusion for
dealing with external storage on free. The ctor/dtor mbuf routines are no
longer used. A zone pointer and length was added to struct mbuf to
simplify free and size calculations.
A number of routines were made much, much simpler by the addition of a
16bit size field. Previously we dependend on calculating the size by
figuring out if it was an ext, pkthdr, or standard mbuf. Ultimately, this
patch moves us closer to having a size agnostic mbuf which we can use to
experiment with different allocation sizes or even backending to malloc
for dynamically sized mbufs.
I would appreciate testing feedback from varied workloads to make sure
there are no bugs before I go forward with this. I have tested only host
oriented networking with a few drivers. It is not anticipated that there
will be any significant incompatibilities introduced with this round but
there is always that possibility.
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