Re: How many copies to get from NIC RX to user read()?

[Nivedita Singhvi <niv@us.ibm.com>]

> So, to make sure I have this right:
> 
> When the data is processed from the NIC
>   tcp_rcv_established() is called in processing it
>     if a user process is waiting on the socket
>       iovec copy data to the user
>     else
>       copy it to receive_queue or backlog_queue

well, we append the skb to the tail of the queue.
this is not a copy operation. (just a few instructions).

> When the user tries read (in any way) a socket
>   iovec copy from receive_queue or backlog_queue
> 
> 
> E.g., if the user is ready for the data, dump it straight from
> SKBs. Else, 
> don't waste SKBs on a lazy (or busy) user and copy the data to a
> queue.

yep.

> If this is right, I'm happy :) If it's wrong, please correct. 
> 
> Thx,
> --Gus

I should add that my reading of the code is hardly
authoritative :). caveat emptor...

thanks,
Nivedita