Re: ia64_do_page_fault shows 19.4% slowdown from notify_die.

[Andi Kleen <ak@suse.de>]

Robin Holt <holt@sgi.com> writes:
 
> 499 nSec/fault ia64_do_page_fault notify_die commented out.
> 501 nSec/fault ia64_do_page_fault with nobody registered.
> 533 nSec/fault notify_die in and just kprobes.
> 596 nSec/fault notify_die in and kdb, kprobes, mca, and xpc loaded.
> 
> The 596 nSec/fault is a 19.4% slowdown.  This is an upcoming OSD beta
> kernel.  It will be representative of what our typical customer will
> have loaded.

With kdb some slowdown is expected.

But just going through kprobes shouldn't be that slow. I guess
there would be optimization potential there.

Do you have finer grained profiling what is actually slow?

 
> Having the notify_page_fault() without anybody registered was only a
> 0.4% slowdown.  I am not sure that justifies the optimize away, but I
> would certainly not object.

Still sounds far too much for what is essentially a call + load + test + return
Where is that overhead comming from?  I know IA64 doesn't like indirect
calls, but there shouldn't any be there for this case.

-Andi