On Mon, May 30, 2011 at 4:07 PM, C K Kashyap <ckkashyap@gmail.com> wrote:
Yes, TCP_NODELAY is a socket option:
Going back to the kernel source:
include/linux/tcp.h:
#define TCP_NODELAY 1 /* Turn off Nagle's algorithm. */
and this:
u8 nonagle : 4,/* Disable Nagle algorithm? */
and looking into the kernel source code:
./fs/ocfs2/cluster/tcp.c: ret = sock->ops->setsockopt(sock, SOL_TCP, TCP_NODELAY,
./net/rds/tcp.c: sock->ops->setsockopt(sock, SOL_TCP, TCP_NODELAY, (char __user *)&val, the above are just two of the examples of how to set TCP_NODELAY in the kernel.
At the userspace level:
http://www.linuxquestions.org/questions/other-*nix-55/how-do-i-disable-the-n...
should be the correct way, except that the poster is attempting to do it in a kernel that does not support it.
As documented in http://linux.die.net/man/7/tcp, the supported kernel is 2.5.71 and onwards.
Okay ... so, the situation I have at hand is that there is this app I cannot modify. I'd like to see its performance with nagle disabled. Is this possible?
as u can see from the above two kernel implementation - each is implementing the algorithm per-socket level, or connection-level, on top of TCP, so, yes, u want to do that is possible. but u will need to write a kernel module, that implement itself as a netfilter module, specifically just for the port that your application is using, and setup socket connection of TCP_NODELAY type. not sure if it will work?
While at it, is there a way to see the socket options of the socket descriptors in a running app? Regards,
Yes, i think so, just sniff out the network packet, and identify the correct bit as according to the header: include/linux/tcp.h: <snip> u16 advmss; /* Advertised MSS */ u8 frto_counter; /* Number of new acks after RTO */ u8 nonagle : 4,/* Disable Nagle algorithm? */ thin_lto : 1,/* Use linear timeouts for thin streams */ thin_dupack : 1,/* Fast retransmit on first dupack */ unused : 2; <snip>
Kashyap
-- Regards, Peter Teoh