Re: Longstanding networking / SMP issue? (duplextest)

[Andi Kleen <ak@suse.de>]

On Thu, Feb 20, 2003 at 08:24:38PM -0800, David S. Miller wrote:
>    From: Andi Kleen <ak@suse.de>
>    Date: Thu, 20 Feb 2003 10:34:22 +0100
> 
>    On Thu, Feb 20, 2003 at 01:20:43AM -0800, Simon Kirby wrote:
>    > Hmm...and this is considered desired behavior?  It seems like an odd way
>    > of handling packets intended to test latency and reliability. :)
>    
>    IP is best-effort. Dropping packets in odd cases to make locking simpler
>    is not unreasonable. Would you prefer an slower kernel?
> 
> True.
> 
> But this is a quality of implementation issue and I doubt the kernel
> would be slower if we fixed this silly behavior.
> 
> Frankly, the locking is due to lazyness, rather than a specific design
> decision.  So let's fix it.

For icmp_xmit_lock it can be only done in a limited fashion - you are
always restricted by the buffer size of the ICMP socket. Also I don't 
know how to lock the socket from BH context nicely - the only simple way
probably is the trick from the retransmit timer to just try again
in a jiffie, but could have nasty queueing up under high load.

Fixing the error drop behaviour of TCP will be somewhat nasty too.

In both cases you'll need a retry timer (unreliable) or an dedicated ICMP 
backlog (complicated)

-Andi