some profiling numbers

[Daniel Berlin]

On Wednesday, June 25, 2003, at 4:52 PM, graydon hoare wrote:

> Daniel Berlin wrote:
>
>> You can't make statements that changing the storage model will or 
>> won't change in terms of performance, or about cache friendliness of 
>> most functions, when 99% of all the structure accesses are happening 
>> in macros that are not accounted for in any of the charts, except in 
>> the functions that call them.
>> You need to know how macro use has changed, the cache miss rate 
>> changes in the macros, etc, in order to properly make general 
>> statements about gcc overall.
>
>
> your initial criticism is true -- I do not account for the code size 
> changes in terms of macro calls, nor do I account for the relative 
> frequency or elapsed time in macro calls. this is because macros are 
> erased (I think) by the time I see them.
Right

> unless dwarf is now preserving macro information and our dwarf reading 
> is missing it,

Well, it can output info about macros (you need -g3), but only to the 
extent that you can do something like p AMACRO(5) in gdb, and have it 
give you the right answer.
It can't stop the preprocessor from expanding them in the source, 
obviously.

>  those symbols don't exist to the profiler. I should put a strong 
> qualification about this in place though, you're right.

>
> your second point I think is not so much true. there are 2 sets of 
> graphs for each cache unit, with different y axes: number of symbols 
> and number of samples. each categorization reflects -- in a slightly 
> different way -- changes to code expanded inline in a function as well 
> as new functions added. neither "ignores" macros; macro code makes 
> load and store requests and consumes clock cycles just like any other 
> code. the tentative conclusion that the cache units are performing 
> reasonably well under garbage collection is simply extrapolation from 
> the fact that neither graph of cycle/miss ratios has a glaring jump to 
> the left that coincides with the introduction of GC.
Granted.

Also, what type of machine was this done on?
I don't remember noticing it written somewhere.
The evidence David Edelsohn gave was for an AIX machine, i forget which 
POWER processor model it was using.

I've also gotten similar numbers to Dave on a g4 running OSX.