Was Collecting SBUs now, Fast compile engines

Björn Lindberg d95-bli.no at spam.nada.kth.se
Fri Jun 7 14:35:12 PDT 2002


Ian Molton wrote:
> 
> On Fri, 07 Jun 2002 22:16:02 +0200
> Björn Lindberg <d95-bli.no at spam.nada.kth.se> wrote:
> 
> >
> > IMO, compiling is mainly dependent on processor speed and cache
> > size/speed as Ian says. Next comes RAM bandwidth, and lastly HDD
> > performance. The last part is "proven" by the fact that the HDD is
> > usually not working very hard at all during compiles, while the CPU
> > is.
> 
> Actually, you got the last two things backward.
> 
> caching, both on the CPU and in the OS come first, and yes, the OSs
> memory cache is in RAM, but even the slowest RAM is faster than a
> harddisc.
> 
> thing is, the data has to get INTO those caches, so unless you have
> compiled the software already, all that data is sitting on the harddisc,
> not in memory.

Of course, but assuming enough RAM it only has to be read /once/ while
it will be processed probably several times.

> so, in order of importance:
> 
> 1) CPU caching
> 2) L2/3 cache (if any)
> 3) OS RAM cache (note: NOT RAM bandwidth - even the DRAM in my 15 yo
> acorn would do here)
> 4) HDD performance, ***especially*** seek time, far more than
> throughput.
> 5) memory bandwidth

You forgot 0) CPU speed, which is the most important factor, IMO. Of
course, we could argue about the significance of CPU speed versus CPU
cache speed/size, but it is not very fruitful, since faster (more
modern) processors generally come with faster/larger caches.


Björn
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