diff options
Diffstat (limited to 'gitlab/issues_text/target_missing/host_missing/accel_missing/1312')
| -rw-r--r-- | gitlab/issues_text/target_missing/host_missing/accel_missing/1312 | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/gitlab/issues_text/target_missing/host_missing/accel_missing/1312 b/gitlab/issues_text/target_missing/host_missing/accel_missing/1312 new file mode 100644 index 000000000..883708f95 --- /dev/null +++ b/gitlab/issues_text/target_missing/host_missing/accel_missing/1312 @@ -0,0 +1,11 @@ +TCP performance problems - GSO/TSO, MSS, 8139 related (Ignores lower MTU from PMTUD/MSS) +Description of problem: +MTU handling on guests using an RTL8139 virtualized NIC is broken; net/hw/8139.c works with a static MTU of 1500b for TCP offloading, leading to low throughput when clients connect from sub 1500MTU networks. PMTUD is ignored, and locking to a lower MTU in the OS mitigates the issue. +Steps to reproduce: +1. Create a guest with an RTL8139 nic +2. Try to retrieve a file from a client behind a sub 1500 MTU link +3. Observe low bandwidth due to retransmits +Additional information: +I just debugged this issue for an NGO which, for whatever reason, had an RTL8139 NIC in their guest. After i finally traced this to the RTL8139, i found this qemu-devel/netdev thread from six years ago, which apparently already debugged this issue and proposed a patch: https://lore.kernel.org/all/20161114162505.GD26664@stefanha-x1.localdomain/ + +I did not test the patch proposed there, but note that `net/hw/8139.c` still looks as discussed in that qemu-devel/netdev thread. As i haven't found a bug report in the archives, i figured you might want to know. |