UDP transmit and no flowid

[Jack Vogel]

Funny, Jeff Pieper and I were just talking about how it seems UDP
performance,
errr is less than optimal, so hey trying something that might help sounds
like
a good idea to me. Will be curious to hear the results!

Cheers,

Jack



On Mon, Mar 3, 2014 at 5:17 PM, Adrian Chadd <adrian.chadd at gmail.com> wrote:

> Hi,
>
> So something I was told about whilst investigating RSS at Netflix was
> that the UDP path doesn't actually get set by anything unless you're
> using flowtable. So, if one doesn't define  flowtable, the transmit
> path congests quite heavily through one TX queue.
>
> I was about to do up a simple hack to do a toeplitz hash in the UDP
> send path before it gets bumped up to ip_output() - that way it can
> set the flowid correctly.
>
> The other option is to do a topelitz hash in ip_output() if m_flowid
> isn't set. The downside there is that we'd have to check whether it's
> actually a TCP, UDP, or IP flow before we assign it a flowid.
>
> In any case, this would likely decongest the transmit path quite a bit
> for UDP send. It's still not completely RSS-y (we would still need to
> line up transmit and receive paths to minimise lock contention) but it
> seems like a necessary first step in that direction.
>
> What do people think?
>
> I'll try this out in the next week or two once I've sorted out my
> employment situation and I can reserve some time on the netperf
> cluster.
>
> (before people ask "why udp?" - I'm kinda fed up with memcached
> performing much worse on freebsd than linux. Since fixing the UDP side
> of things requires a subset of the same work needed for TCP, I figure
> we should tackle UDP first.)
>
> Thanks,
>
>
> -adrian
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