[openib-general] [PATCH/RFC] IB/ipoib: add selective tx signaling

[Moni Shoua]

Michael S. Tsirkin wrote:
>>I don't think that holding the skb too long is a trigger for somethink. 
> 
> 
> 
> Are you sure? We are not talking about too long here - unsignalled TX packet
> will never get a completion. As far as I can see, __kfree_skb will
> 1. call dst_release - so this patch might keep a reference on dst indefinitely?
I don't think that holding dst too long is unsafe. Imagine a constant stream of packets
to the same destination. In this case will always be a reference to a dst struct.
> 2. call skb->destructor if not NULL - this is responsible for socket buffer
>    accounting
I addressed the issue of the socket buffer accounting in the openning message.
I don't see it as a problem but more than an note to the user. Don't you think?
> 3. Releases reference to lots of other objects related to netfiltering
> 
> Are you sure keeping all these references indefinitely is safe?
I can't say I'm 100% sure but please see my comment below.
> 
A comment regarding the word "indefinitely" - I understand that theoretically there
is a chance that no packet will be sent through the ib interface causing unnecessary resource
allocation as you described. I think however that the chance for that is very small and 
that the price is worth for gaining performance increase. This is true of course if the 
penalty is just resource allocation and not system safety. In this context I can say that my 
tests didn't cause any bad system behavior and my senses tell me there shouldn't be any.
However, I would be glad to learn more from those who know more.