SIO_LOOPBACK_FAST_PATH must be set on the socket passed to accept. The way I think about this is the socket instance passed to listen represents the port while the socket instance passed to accept represents a single TCP stream. SIO_LOOPBACK_FAST_PATH has no effect when applied to a port, but does have an effect when applied to a TCP stream.
Given that we are open to suggestions for a better organization of the code to set SIO_LOOPBACK_FAST_PATH on the sockets passed to accept. Thanks, Kirk Software Design Engineer Microsoft Open Technologies, Inc. MS Open Tech is hiring (http://aka.ms/msopentechjobs)! Ask me for details if anyone you know is interested. From: Alan Bateman [mailto:alan.bate...@oracle.com] Sent: Wednesday, September 24, 2014 12:51 AM To: Martin Sawicki (MS OPEN TECH); net-dev@openjdk.java.net Cc: Valery Kopylov (Akvelon); Kirk Shoop (MS OPEN TECH); nio-dev Subject: Re: Taking advantage of TCP Loopback fast path in Windows On 24/09/2014 02:19, Martin Sawicki (MS OPEN TECH) wrote: Hello We're proposing an improvement to the OpenJDK which enables users to take advantage of the TCP loopback fast path mechanism in Windows for significantly higher performance of sockets whose both end points are on the same machine. This is especially relevant in distributed server-side/cloud scenarios, such as Hadoop. We have the code figured out and tested internally. I've uploaded our webrev package here (too big to send as an attachment): https://openjdkcontrib.blob.core.windows.net/tcploopback/webrev-20140918.zip The crux of the change lies in enabling the SIO_LOOPBACK_FAST_PATH IOCTL flag on each socket creation call in Windows. As for activating this optimization, we're proposing the conservative approach of keeping it off by default and adding a command line argument to activate it: -Dwindows.enableFastLocalTcpLoopback=true | false (IMHO though, it'd be great to eventually just have it on by default). We'd appreciate a review and acceptance of this improvement. And, as we are new in the OpenJDK community and this may as well be our first contribution to Java, I apologize for any steps in the submission process that I may have missed here and would appreciate guidance as needed. Welcome, it's good to see Microsoft engineers on OpenJDK lists. If I understand this ioctl correctly then it should only need to be set once on a SOCKET. I'm curious about the listener oriented channels (ServerSocketChannel etc.) where it is being set prior to each call to accept. Is this needed? If not then I assume that we can just set it when creating the SOCKET, sun.nio.ch.Net.socket0 of SocketChannel, ServerSocketChannel, etc. You'll see that it already goes some Windows specific setup and that might be the place to put it (and I think should eliminate the need for most of the changes to the NIO code). -Alan
