netdev - Re: Make TCP work better with re-ordered frames?

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Message-ID: <1463581760.18194.114.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Wed, 18 May 2016 07:29:20 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: Make TCP work better with re-ordered frames?

On Wed, 2016-05-18 at 07:00 -0700, Ben Greear wrote:
> We are investigating a system that has fairly poor TCP throughput
> with the 3.17 and 4.0 kernels, but evidently it worked pretty well
> with 3.14 (I should be able to verify 3.14 later today).
> 
> One thing I notice is that a UDP download test shows lots of reordered
> frames, so I am thinking maybe TCP is running slow because of this.
> 
> (We see about 800Mbps UDP download, but only 500Mbps TCP, even when
>   using 100 concurrent TCP streams.)
> 
> Is there some way to tune the TCP stack to better handle reordered frames?

Nothing yet. Are you the sender or the receiver ?

You really want to avoid reorders as much as possible.

Are you telling us something broke in networking layers between 3.14 and
3.17 leadings to reorders ?