Home » Mailing list archives » linux-kernel » 2007 » November » 2

Re: bizarre network timing problem

!MAILaRCHIVE_VOTE_RePLACE
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
[view in full thread]
From: Rick Jones <rick.jones2@...>
To: Felix von Leitner <felix-linuxkernel@...>
Cc: Chuck Ebbert <cebbert@...>, <linux-kernel@...>, Netdev <netdev@...>
Subject: Re: bizarre network timing problem
Date: Friday, November 2, 2007 - 6:33 pm

Felix von Leitner wrote:
 >

I wonder if the ack 16384 win 125 not updating the window is part of it?  With a 
  window scale of 7, the advertised window of 125 is only 16000 bytes, and it 
looks based on what follows that TCP has another 16384 to send, so my guess is 
that TCP was waiting to have enough window, the persist timer expired and TCP 
then had to say "oh well, send what I can"  Probably a coupling with this being 
less than the MSS (16396) involved too.


Notice that an ACK comes-back with a zero window in it - that means that by this 
point the receiver still hasn't consumed the 16384+16000 bytes sent to id.


Now the receiver has pulled some data, on the order of 96*128 bytes so TCP can 
now go ahead and send the remaining 384 bytes.


I'll bet that 96 * 128 is 12288 and we have another persist timer expiring.

I also wonder if the behaviour might be different if you were using send() 
rather than sendfile() - just random musings...


And it wasn't waiting for an ACK/window-update.  You could try:

ifconfig lo mtu 1500

and see what happens then.


Joy.


Well, a wise old engineer tried to teach me that the proper spelling is ass-u-me 
:) so just for grins, you might try the TCP_RR test anyway :)  And even if your 
application is correct (although I wonder why the receiver isn't sucking 
data-out very quickly...) if you can reproduce the problem with netperf it will 
be easier for others to do so.

rick jones
-
Previous message: [thread] [date] [author]
Next message: [thread] [date] [author]
Messages in current thread:
bizarre network timing problem, Felix von Leitner, (Wed Oct 17, 4:51 pm)
Re: bizarre network timing problem, Chuck Ebbert, (Wed Oct 17, 5:17 pm)
Re: bizarre network timing problem, Felix von Leitner, (Wed Oct 17, 6:00 pm)
Re: bizarre network timing problem, Rick Jones, (Wed Oct 17, 6:16 pm)
Re: bizarre network timing problem, Felix von Leitner, (Thu Oct 18, 5:42 am)
Re: bizarre network timing problem, Rick Jones, (Thu Oct 18, 1:22 pm)
Re: bizarre network timing problem, Felix von Leitner, (Fri Nov 2, 6:11 pm)
Re: bizarre network timing problem, Rick Jones, (Fri Nov 2, 6:33 pm)
Re: bizarre network timing problem, Felix von Leitner, (Fri Nov 2, 6:38 pm)
Re: bizarre network timing problem, Rick Jones, (Fri Nov 2, 6:58 pm)
Re: bizarre network timing problem, Felix von Leitner, (Fri Nov 2, 7:23 pm)
Re: bizarre network timing problem, Rick Jones, (Tue Nov 6, 5:12 pm)