Re: [Ksummit-2005-discuss] Summary of 2005 Kernel Summit Proposed Topics

[Dmitry Yusupov <dmitry_yus@yahoo.com>]

On Sat, 2005-03-26 at 22:46 -0800, David S. Miller wrote:
> On Sat, 26 Mar 2005 22:33:01 -0800
> Dmitry Yusupov <dmitry_yus@yahoo.com> wrote:
> 
> > i.e. TCP stack should call NIC driver's callback after all SKB data
> > been successfully copied to the user space. At that point NIC driver
> > will safely replenish HW ring. This way we could avoid most of memory
> > allocations on receive.
> 
> How does this solve your problem?  This is just simple SKB recycling,
> and it's a pretty old idea.

I know. it is very old idea.

> TCP packets can be held on receive for arbitrary amounts of time.

I'm thinking about mixing existing way of doing things with guarantied
SKB recycling. It should help to storage stacks to make a progress on
receive at least.

> This is especially true if data is received out of order or when
> packets are dropped.  We can't even wake up the user until the
> holes in the sequence space are filled.
> 
> Even if data is received properly and in order, there are no hard
> guarentees about when the user will get back onto the CPU to
> get the data copied to it.
> 
> During these gaps in time, you will need to keep your HW receive
> ring populated with packets.

ethernet flow-control must take care this case.

If driver's replenish logic could mix alloc_skb/netif_rx and SKB
recycling than pause frames should never happen even with gige+
interfaces.