netdev - Re: Poor thunderbolt-net interface performance when bridged

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250526080956.7f64a5f5@hermes.local>
Date: Mon, 26 May 2025 08:09:56 -0700
From: Stephen Hemminger <stephen@...workplumber.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Ricard Bejarano <ricard@...arano.io>, Mika Westerberg
 <mika.westerberg@...ux.intel.com>, netdev@...r.kernel.org,
 michael.jamet@...el.com, YehezkelShB@...il.com, andrew+netdev@...n.ch,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com
Subject: Re: Poor thunderbolt-net interface performance when bridged

On Mon, 26 May 2025 16:28:23 +0200
Andrew Lunn <andrew@...n.ch> wrote:

> > > Simple peer-to-peer, no routing nothing. Anything else is making things
> > > hard to debug. Also note that this whole thing is supposed to be used as
> > > peer-to-peer not some full fledged networking solution.  
> >   
> > > Let's forget bridges for now and anything else than this:
> > >  Host A <- Thunderbolt Cable -> Host B  
> > 
> > Right, but that's precisely what I'm digging into: red->blue runs at line speed,
> > and so does blue->purple. From what I understand about drivers and networking,
> > it doesn't make sense then that the red->blue->purple path drops down so much in
> > performance (9Gbps to 5Mbps)  
> 
> Agreed.
> 
> Do the interfaces provide statistics? ethtool -S. Where is the packet
> loss happening?
> 
> Is your iperf testing with TCP or UDP?  A small amount of packet loss
> will cause TCP to back off a lot. Also, if the reverse direction is
> getting messed up, ACKs are getting lost, TCP will also stall.
> 
> Maybe try a UDP stream, say 500Mbs. What is the packet loss? Try the
> reverse direction, what is the packet loss. Then try --bidir, so you
> get both directions at the same time.
> 
> 	Andrew
> 

What is MTU? Bridging is L2 and if MTU does not match packets are
silently dropped.