Re: [PATCH] NET_DMA: free skbs periodically

[David Miller]

From: "Steven J. Magnani" <steve@xxxxxxxxxxxxxxx>
Date: Tue, 16 Mar 2010 10:22:44 -0500

> Under NET_DMA, data transfer can grind to a halt when userland issues a
> large read on a socket with a high RCVLOWAT (i.e., 512 KB for both).
> This appears to be because the NET_DMA design queues up lots of memcpy 
> operations, but doesn't issue or wait for them (and thus free the 
> associated skbs) until it is time for tcp_recvmesg() to return. 
> The socket hangs when its TCP window goes to zero before enough data is 
> available to satisfy the read.
> 
> Periodically issue asynchronous memcpy operations, and free skbs for ones 
> that have completed, to prevent sockets from going into zero-window mode.
> 
> Signed-off-by: Steven J. Magnani <steve@xxxxxxxxxxxxxxx>

Can one of the NET DMA folks review this.

It's a pretty fundamental problem with how this stuff works
it seems.
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