Re: Kernel hooks just to get rid of copy_[to/from]_user() and syscall overhead?

[Richard B. Johnson]

On Fri, 10 Jan 2003, Mihnea Balta wrote:

> Hi,
> 
> I have to implement a system which grabs udp packets off a gigabit connection, 
> take some basic action based on what they contain, repack their data with a 
> custom protocol header and send them through a gigabit ethernet interface on 
> broadcast.
> 
> I know how to do this in userspace, but I need to know if doing everyting in 
> the kernel would show a considerable speed improvement due to removing 
> syscall and memory copy overhead. The system will be quite stressed, having 
> to deal with around 15-20000 packets/second.
> 
> I didn't want to start this e-mail with an excuse, so I delayed it until here 
> :). I appologise if this isn't the right place to ask, it seemed that way to 
> me. I wasn't able to find sufficient and coherent information about this 
> issue on the internet or on this mailing list's archives, so I decided to ask 
> you people directly.
> 
> Thanks for your time,
> Mihnea Balta
> 

I think you should do everything in kernel space, with a user-mode
interface for non-realtime control, i.e., what characteristics
of UDP packets are being "filtered". You just make a module that
contains what you need, with an ioctl() hook to control it.

That way, data from your gigabit interface(s) never has to get to
"user-space" at all.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Why is the government concerned about the lunatic fringe? Think about it.