From mboxrd@z Thu Jan 1 00:00:00 1970
From: htmldeveloper@gmail.com (Peter Teoh)
Date: Mon, 30 May 2011 16:34:58 +0800
Subject: Disabling nagle algorithm
In-Reply-To:
References:
Message-ID:
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org
On Mon, May 30, 2011 at 4:07 PM, C K Kashyap 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:
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;
> Kashyap
--
Regards,
Peter Teoh