Re: [NET]: Prevent multiple qdisc runs

[jamal <hadi@cyberus.ca>]

Herbert,

On Mon, 2006-19-06 at 23:42 +1000, Herbert Xu wrote:
> Hi Jamal:
> 
> On Mon, Jun 19, 2006 at 09:33:51AM -0400, jamal wrote:
[..]
> 
> Actually I discovered the problem only because the generic segmentation
> offload stuff that I'm working on needs to deal with the situation where
> a super-packet is partially transmitted.  Requeueing causes all sorts of
> nasty problems so I chose to keep it within the net_device structure.
>
> To do so requires qdisc_run to be serialised against each other.  I then
> found out that we want this anyway because otherwise the requeued packets
> could be reordered.
> 

Ok, I am trying to visualize but having a hard time:
Re-queueing is done at the front of the queue to maintain ordering
whereas queueing is done at the front (i.e it is a FIFO). i,e
even if p2 comes in and gets queued while p1 is being processed,
requeueing of p1 will put it infront of p2.
Your super-packet issue may be different though ..

> > Also: what happens to the packet that comes in from either local or is
> > being forwarded and finds the qdisc_is_running flag is set? I couldnt
> > tell if the intent was to drop it or not. The answer for TCP is probably
> > simpler than for packets being forwarded.
> 
> The qdisc_is_running only prevents qdisc_run from occuring (because it's
> already running), it does not impact on the queueing of the packet.
> 

I will wait for your answer on the other part before responding to this.

cheers,
jamal