[fpc-devel] Re: Compiler bottlenecks

Jonas Maebe jonas.maebe at elis.ugent.be
Thu Jul 15 10:26:18 CEST 2010

Hans-Peter Diettrich wrote on Thu, 15 Jul 2010:

> Jonas Maebe schrieb:
> When the file resides in the OS file cache, no page faults will  
> occur unless the file was removed from the cache. If not, every  
> access request has to do disk I/O, resulting in process switching  
> etc., so that the page faults are neglectable.

That is only true if you get at most as many page faults as you  
perform "read" system calls.

>> Then just read it into a buffer in one shot.
> That's just what I suggested, for a first test :-)

Just increasing the buffer size by itself does not have any noticeable  
effects on the compilation speed (I benchmarked it in the past).

>> a) the memory management overhead primarily comes from allocating  
>> and freeing machine instruction (and to a lesser extent node tree)  
>> instances
>> b) the string copy cost I mentioned primarily comes from getting  
>> symbol names for the purpose of generating rtti and assembler  
>> symbol names
> May be, we'll see...

Those facts come from profiling runs. That does not mean that nothing  
can be optimised in the scanner/parser, but the bottleneck routines I  
posted are unrelated.


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