On Mon, Apr 09, 2018 at 01:14:58PM +0000, David Laight wrote: > From: kpark3...@gmail.com > > Sent: 09 April 2018 12:59 > > > > The old arch_within_stack_frames which used the frame pointer is > > now reimplemented to use frame pointer unwinder apis. So the main > > functionality is same as before. > > How much slower does this make the code? > Following stack frames using %bp is reasonably quick. > I can't imagine some of the other unwinder APIs being any where > near that fast. > While fine for fault tracebacks, using them during usercopy > is likely to have measurable performance impact.
Agreed, using the unwind interface is going to be quite a bit slower than the current manual approach. So this patch has only drawbacks and no benefits. The only benefit would be if you used the unwind API in a generic manner, such that it also worked for the ORC unwinder. But even then I think we'd need to see performance numbers, with both FP and ORC, to see how bad the impact is on usercopy. -- Josh
