I'm seeing similar behavior on multiple physical hosts running 4.15.0-36-generic. The TCP window size only appears to grow very slightly (from initial of 224 to around 1400) during the entire length of the transfer.
Downgrading to 4.15.0-34-generic fixes the issue for me - TCP window size continues to grow until it is around 24k. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1796895 Title: Kernel 4.15.0-36 network performance regression Status in linux package in Ubuntu: Confirmed Status in linux source package in Bionic: Confirmed Bug description: Hardware: HP DL380 Gen 7 server with Gigabit interface. Ubuntu release: 18.04.1 Since upgrading from 4.15.0-33 to 4.15.0-36, I have noticed a dramatic slowdown in TCP over IPv6. Set up: two servers, Server A in US on Ubuntu 18.04.1, Server B in Europe. Test: Sending 400MB over TCP from Server B to Server A. With 4.15.0-33 on Server A, the transfer is completed in 24 seconds, with average speed of 139 mbps. With 4.15.0-36 on Server A, the same amount of data is transferred in 369 seconds, average speed less than 9 mbps. Looking at the result from tcpdump, I see that the there is a big difference in the TCP Window size. With 3.15-0.33 the TCP window size is around 30000. But with 3.15-0.36, the window size is only 734. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1796895/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
