On Mon, May 30, 2011 at 4:07 PM, C K Kashyap <ckkashyap@xxxxxxxxx> 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-nagle-algorithm-in-enterprise-linux-3-kernel-ver-2-4-21-4-a-556170/ >> >> 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 _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
