Re: [PATCH] Implementation of the sendgroup() system call

[Andi Kleen <andi@firstfloor.org>]

Elad Lahav <elahav@uwaterloo.ca> writes:

> The attached patch contains an implementation of sendgroup(), a system
> call that allows a UDP packet to be transmitted efficiently to
> multiple recipients. Use cases for this system call include
> live-streaming and multi-player online games.
> The basic idea is that the caller maintains a group - a list of IP
> addresses and UDP ports - and calls sendgroup() with the group list
> and a common payload. Optionally, the call allows for per-recipient
> data to be prepended or appended to the shared block. The data is
> copied once in the kernel into an allocated page, and the
> per-recipient socket buffers point to that page. Savings come from
> avoiding both the multiple calls and the multiple copies of the data
> required with regular socket operations.

My guess it's more the copies than the calls? It sounds like
you want sendfile() for UDP. I think that would be a cleaner solution
than such a specific hack for your application. It would
have the advantage of saving the first copy too and be 
truly zero copy on capable NICs.

Or perhaps simple send to a local multicast group and let
some netfilter module turn that into regular UDP.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only.