I don't disagree, but it makes it an apples an oranges comparison. It introduces the variables of how linux vs windows deals with TCP (not withstanding that linux 2.x vs 3. might have some internal ipv4 changes, but youre recommendation is to upgrade anyway, so that's fine) but also changes in the webserver.. It seems like the changes are hard coded into the compiled kernel, so there's no way to simply change configuration flags?
That said, thanks for the post, and I'll definitely be tcpdumping in the upcoming week and reading some more about slowstart!
Maybe testing with net.ipv4.tcp_slow_start_after_idle 0 vs 1 would make a cleaner comparison?
I totally agree with the concern, but the only way for a clean comparison here would be for me to spin up a new VM. I observe the exact same patterns as I get from the windows VM on our Linux 2.x prod box so assume they are the same.
There were a slew of TCP changes leading up to the 3 branch which included changing the default congestion control algorithm to cubic.
slow start after idle does not really play part here. The test is for a clean/new connection.
I am no expert but it is possible I could lower my IW on my 3.2 box to 3 to demonstrate the same pattern, however that too is not a clean comparison.
If my sys admins push me I may set up another VM to demonstrate this.
Thanks again for your blog post and comments in this thread! Experiments where you already are really confident about the conclusions are pretty silly, but I feel like despite that being skeptical in general to posts on the internet has value. I haven't investigated yet, but if I do investigate clear benefits of slow start and can make a corroborating case, i'll be happy to correspond and write it up in a blog post.. No promises though :)
