Andrew Gallatin wrote:
Andre,
I meant to ask: Did you try 16KB jumbos? Did they perform
any better than page-sized jumbos?
No, I didn't try 16K jumbos. The problem with anything larger than
page size is that it may look contigous in kernel memory but isn't
in physical memory. Thus you need the same number of descriptors
for the network card as with page sized (4K) clusters.
Also, if we're going to change how mbufs work, let's add something
like Linux's skb_frag_t frags[MAX_SKB_FRAGS]; In FreeBSD parlence,
this embeds something like an array of sf_bufs pointers in mbuf. The
big difference to a chain of M_EXT mbufs is that you need to allocate
only one mbuf wrapper, rather than one for each item in the list.
Also, the reference is kept in the page (or sf_buf) itself, and the
data offset is kept in the skbbuf (or mbuf).
We are not going to change how mbufs work.
This allows us to do cool things like allocate a single page, and use
both halves of it for 2 separate 1500 byte frames. This allows us to
achieve *amazing* results in combination with LRO, because it allows
us to do, on average, many fewer allocations per byte. Especially in
combination with Linux's "high order" page allocations. Using order-2
allocations and LRO, I've actually seen 10GbE line rate receives on a
wimpy 2.0GHz Athlon64.
I have just started tackling the receive path. Lets see what comes out
of it first before we jump to conclusions.
--
Andre
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