Question: kprobe fault handler

[Keshavamurthy Anil S]

On Tue, May 10, 2005 at 04:34:42PM -0400, Ananth N Mavinakayanahalli wrote:
> On Tue, May 10, 2005 at 12:35:48PM -0700, Keshavamurthy, Anil S wrote:

> I think the best explaination as to why that hook is needed in the
> fast-path was given by Dave Miller. Please see:
> 
> http://marc.theaimsgroup.com/?l=linux-kernel&m=109898820219611&w=2
Thanks for the link.

> 
> The overhead is: notifier_call_chain() -> kprobe_running() check in
> kprobe_exceptions_notify(). And, if any other debugger/utility 
> (eg., kgdb) is using the die_notifier, it will also be invoked.

So you are saying that for every page fault, the overhead is
notifier_call_chain()->kprobe_exception_notify()->kprobe_running(), 
I agree this is very small when you don't have any kprobes registered.

Imagine a case where 1000 Kprobes are registered and in this
case for every pagefault, notifier_call_chain() has to loop for 1000
times, this seems to me an overkill. Please correct me if I am wrong.


-Anil