Unable to turn TSO on on virtual interfaces on RHEL 6.5

21시 04분 2014년 2월 10일 업데이트

문제

¶When booting RHEL 6.5 kernel 2.6.32-431.el6.x86_64, this message appears in the console/dmesg:

lo: Dropping TSO features since no CSUM feature.
(null): Dropping TSO features since no CSUM feature.
(null): Dropping TSO6 features since no CSUM feature.
rhevm: Dropping TSO features since no CSUM feature.

환경

Red Hat Enterprise Linux (RHEL) 6.5
Any virtual interface

해결

¶This issue was partially addressed by kernel erratum RHBA-2014:0004. Upgrading your kernel to version 2.6.32-431.3.1.el6 will solve the problem for most virtual interface types including the loopback interface (lo), plain bonded interfaces (e.g. bondN) and plain VLAN interfaces (e.g. ethX.NNN).

¶It was discovered that RHBA-2014:0004 missed one use case: VLAN interfaces on top of bonded interfaces (e.g. bondX.NNN). At the time of this writing, the problem with this particular use case is under investigation by Red Hat Engineering. If you're affected by this use case please contact Red Hat Support to get assistance.

근본 원인

¶A change on how offloading flags are computed together rendered TSO and TSO6 unable to stay on for virtual interfaces, like bonding, bridges and even loopback.

¶The release notes for RHBA-2014:0004 explain:

* Previously, the bonding driver did not support TCP segmentation offloading
(TSO). As a consequence, the performance decreased significantly, and the
"ethtool -k bondX" command reported that the TSO was disabled, although the
slave device had the TSO enabled. The following message appeared in the kernel
log: "Dropping TSO features since no CSUM". The problem affected also bridges
and loopback interfaces. The underlying source code has been modified to ensure
that the bonding module does not drop TSO features for NO_CSUM devices. As a
result, the aforementioned performance problem no longer occurs. (BZ#1037812)

진단 단계

¶Check your dmesg log for messages like:

lo: Dropping TSO features since no CSUM feature.
(null): Dropping TSO features since no CSUM feature.
(null): Dropping TSO6 features since no CSUM feature.
(null): Dropping TSO features since no CSUM feature.
(null): Dropping TSO6 features since no CSUM feature.
rhevm: Dropping TSO features since no CSUM feature.