Instrumenting context-switching

[Perry Cheng <perryche at us dot ibm dot com>]

Instrumenting the context switch code has long been delicate.   I can't 
seem to find any help on this particular topic on the wiki (specifically, 
the examples).

In the past, following some hints from old docs and mailing list, it has 
been enough to instrument the __switch_to method to get the prev and next 
tasks.  The method one level higher is switch_to which, being a macro, is 
not instrumentable.  Lately, I've switched from an older i386 kernel to a 
new x86_64 kernel and now __switch_to no longer is instrumentable with 
kprobes.   The higher-level context_switch itself does not seem probe-able 
because it is a static inline method.  Even higherup, we have the call to 
context_switch from schedule but instrumenting that would require using a 
specific line number which seems rather fragile because of greater 
reliance of debugging code and susceptibility to kernel code change.

So, on an x86_64 kernel, how do I instrument this method?

Perry