Re: [Valgrind-developers] valgrind: r5275 - trunk/coregrind/m_dispatch

[Julian S. <js...@ac...>]

> This seems like a good choice since the survey found that aroun 40% of
> users clearly identified themselves as using P4s, as opposed to about 5%
> for P3s.

incl/decl are recommended don't-uses on P4s.

Not that it made any measurable difference at all.

I did write a small program to measure the branch-mispredict cost
on P4, and found it to be 21 cycles.  I also established that P4 
can only predict one branch target address for an indirect jump
(alternating between 2 different ones is worse, and cycling through
4 gives you the full 21-cycle hit).  What this means is that
each bb dispatch stalls for 21 cycles, which at an IPC of 0.8 is
worth 16 ish insns.  Bad.

J