Messages in this thread | | | Date | Thu, 18 Oct 2007 10:22:18 -0700 | From | Rick Jones <> | Subject | Re: bizarre network timing problem |
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Felix von Leitner wrote: >>the packet trace was a bit too cooked perhaps, but there were indications >>that at times the TCP window was going to zero - perhaps something with >>window updates or persist timers? > > > Does TCP use different window sizes on loopback? Why is this not > happening on ethernet?
I don't think it uses different window sizes on loopback, but with the autotuning it can be difficult to say a priori what the window size will be. What one can say with confidence is that the MTU and thus the MSS will be different between loopback and ethernet.
> > How could I test this theory?
Can you take another trace that isn't so "cooked?" One that just sticks with TCP-level and below stuff?
If SMB is a one-request-at-a-time protocol (I can never remember), you could simulate it with a netperf TCP_RR test by passing suitable values to the test-specific -r option:
netperf -H <remote> -t TCP_RR -- -r <req>,<rsp>
If that shows similar behaviour then you can ass-u-me it isn't your application. One caveat though is that TCP_CORK mode in netperf is very primitive and may not match what you are doing, however, that may be a good thing.
http://www.netperf.org/svn/netperf2/tags/netperf-2.4.4/ or ftp://ftp.netperf.org/netperf/
to get the current netperf bits. It is also possible to get multiple transactions in flight at one time if you configure netperf with --enable-burst, which will then enable a test-specific -b option. With the latest netperf you cna also switch the output of a TCP_RR test to bits or bytes per second a la the _STREAM tests.
rick jones
> > My initial idea was that it has something todo with the different MTU on > loopback. My initial block size was 16k, but the problem stayed when I > changed it to 64k. > > Felix
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