RE: TCP reaching to maximum throughput after a long time

On Wed, Apr 13, 2016 at 17:32:29, Neal Cardwell wrote:

Miller; Eric Dumazet; Nandita Dukkipati; open list; Kama, Meirav
Subject: Re: TCP reaching to maximum throughput after a long time

I like the idea to disable hystart ack-train.


Yaniv, can you please re-run your test with CUBIC in three different
scenarios:

a) echo 0 > /sys/module/tcp_cubic/parameters/hystart_detect

This fixes the issues, got to max throughput immediately. 

b) echo 1 > /sys/module/tcp_cubic/parameters/hystart_detect

This shows the same results as before, starting low and increasing slowly.

c) echo 2 > /sys/module/tcp_cubic/parameters/hystart_detect

This gets us a bit higher at the beginning, but never (waited ~60 sec) goes to the max.


Appreciate your help on this.
Yaniv

This should help us isolate whether the hystart ack-train algorithm is 
causing problems in this particular case.

Thanks!
neal



On Tue, Apr 12, 2016 at 11:32 PM, Eric Dumazet 
[off-list ref]
wrote:


	On Tue, 2016-04-12 at 20:08 -0700, Yuchung Cheng wrote:

	> based on the prev thread I propose we disable hystart ack-train. It 
is
	> brittle under various circumstances. We've disabled that at Google 
for
	> years.

	Right, but because we also use sch_fq packet scheduler and pacing ;)