tree 724151d30c232e38ea947705986cfe60a3359241
parent f5d410f2ea7ba340f11815a56e05b9fa9421c421
author Steven J. Magnani <steve@digidescorp.com> 1268716964 +0000
committer David S. Miller <davem@davemloft.net> 1269120542 -0700

NET_DMA: free skbs periodically

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@digidescorp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>