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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-6005a6e3ca0sm16582995a12.42.2025.05.26.08.10.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 May 2025 08:10:03 -0700 (PDT) Date: Mon, 26 May 2025 08:09:56 -0700 From: Stephen Hemminger To: Andrew Lunn Cc: Ricard Bejarano , Mika Westerberg , netdev@vger.kernel.org, michael.jamet@intel.com, YehezkelShB@gmail.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com Subject: Re: Poor thunderbolt-net interface performance when bridged Message-ID: <20250526080956.7f64a5f5@hermes.local> In-Reply-To: References: <20250523110743.GK88033@black.fi.intel.com> <353118D9-E9FF-4718-A33A-54155C170693@bejarano.io> <20250526045004.GL88033@black.fi.intel.com> <5DE64000-782A-492C-A653-7EB758D28283@bejarano.io> <20250526092220.GO88033@black.fi.intel.com> <4930C763-C75F-430A-B26C-60451E629B09@bejarano.io> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Mon, 26 May 2025 16:28:23 +0200 Andrew Lunn 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.