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

[Avi Kivity]

Andi Kleen wrote:
> Elad Lahav <elahav@xxxxxxxxxxxx> 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.
>   

An aio udp send could accomplish both multiple packets per call, and 
zero-copy, without adding new syscalls.  You could send the same packet 
to multiple recipients, or multiple packets to the same recipicent, or 
combinations thereof.

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

Sounds hacky and rooty.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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