Re: Reasonable L1 cache miss rate for gcc

[Daniel Berlin <dberlin@dberlin.org>]

On Sun, 11 Aug 2002, Daniel Jacobowitz wrote:

> On Sun, Aug 11, 2002 at 01:12:39AM -0400, Daniel Berlin wrote:
> > What is a reasonable L1 cache miss rate (for memory loads 
> > only not instructions) is for a P4 running GCC?
> > 
> > I have the exact figures, but without some idea of what reasonable would 
> > be, i have no idea how *bad* it is.
> > 
> > Percentage wise, it's a 14-25% miss rate (depending on input).
> > 
> > Of course, I really want to know about L2's, but the file describing all  
> > the available p4 pmcs says:
> 
> > Sigh.
> > 
> > Someone with a PIII should be able to get oprofile to give us some l2 
> > numbers.
> 
> Assuming that I actually figured out what these numbers mean...
> I remade insn-*.o in a gcc HEAD build with two compilers (no
> optimization):
> 
> 		DATA_MEM_REFS		L2_LINES_IN	  L2 Miss %
> GCC 2.95.3 cc1	 4.32e9			  3.23e7	  0.7%
> GCC 3.1.1 cc1	 7.0265e9		  6.3e7		  0.8%
> 
> Something tells me I've got the wrong numbers, though... those look far
> too low.  If someone cares to enlighten me on the right counters to
> use, I'll be more thorough.

Make sure it compiles with optimization on.

But, otherwise, it's quite possible those aren't too low.
Remember it can only take an L2 miss when it misses L1.
So comparing complete data refs to L2 misses will always give you very 
low numbers.