CONFIG_FTRACE works by having the compiler insert a call to mcount() into the beginning of every kernel function. The author has quantified this overhead at 15–18% even for a completely empty mcount() function <http://lkml.org/lkml/2008/8/7/270>; the actual overhead is greater because the real mcount() function needs to test whether ftrace is enabled before returning.
CONFIG_DYNAMIC_FTRACE reduces this overhead to nearly zero by patching over the mcount() calls with NOPs at runtime, but obviously because of the bug this feature can no longer be used. (That’s all with ftrace disabled at runtime. When it is enabled, the overhead jumps to about 5000%, which more or less grinds the system to a halt.) So I would say that it is important to turn CONFIG_FTRACE off for the release, if that’s still possible. -- Major memory corruption bug in 2.6.27 CONFIG_DYNAMIC_FTRACE https://bugs.launchpad.net/bugs/284109 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
