Re: Much improved sosend_*() functions


Andre Oppermann writes:
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.

But it would allow you to do one copyin, rather than 4. I
don't know how much this would help, but it might be worth
looking at.

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.

It could be mbufs are cheaper to get than skbs and pages on linux,
but I doubt it. FWIW, linux has an skb chaining mechanism
(frag_list). My first LRO experiment was based on allocating "normal"
skbs and chaining them. That maxed out at around 5.2Gb/s (on the same
hardware I see line rate on).

Drew
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Relevant Pages

  • Re: Much improved sosend_*() functions
    ... Did you try 16KB jumbos? ... only one mbuf wrapper, rather than one for each item in the list. ... combination with Linux's "high order" page allocations. ... It could be mbufs are cheaper to get than skbs and pages on linux, ...
    (freebsd-current)
  • Re: Much improved sosend_*() functions
    ... any better than page-sized jumbos? ... only one mbuf wrapper, rather than one for each item in the list. ... achieve *amazing* results in combination with LRO, ... combination with Linux's "high order" page allocations. ...
    (freebsd-current)
  • Re: Much improved sosend_*() functions
    ... any better than page-sized jumbos? ... only one mbuf wrapper, rather than one for each item in the list. ... achieve *amazing* results in combination with LRO, ... combination with Linux's "high order" page allocations. ...
    (freebsd-net)
  • Re: Much improved sosend_*() functions
    ... > Andrew Gallatin wrote: ... Did you try 16KB jumbos? ... >> 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. ...
    (freebsd-current)
  • Re: Much improved sosend_*() functions
    ... > Andrew Gallatin wrote: ... Did you try 16KB jumbos? ... >> 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. ...
    (freebsd-net)