Re: [boost] Re: Problems with boost on Cray C++ release 3.6

From: Matthias Troyer (troyer_at_[hidden])
Date: 2003-01-18 14:52:08

On Saturday, January 18, 2003, at 07:36 PM, Daniel Yerushalmi wrote:

> <SNIP>
> I'll try to do it at least once to see which parts of boost we can use,
> and see how much CPU time this gobbles up. If it is not too much, I
> will talk to our sysadmins if they would allow me to do it about once a
> month. I don't think that testing more often would be possible, since
> already compiling only the filesystem library takes about 15 minutes.
> </SNIP>
> ?
> How come?  on my lowly PC it take less then a minute... (compiling 
> just the
> filesystem)
>
> /Daniel Yerushalmy

A Cray is optimized for peak-floating point performance even for 
out-of-cache codes and optimized for that and not for compile time. 
There are several reasons why it is slow:

i) in order to optimize the runtime performance the machine does not 
use virtual memory for a process, which makes dynamic allocation very 
slow. If I need more memory than was allocated initially, the whole 
process is swapped out and has to wait for a later time slice when more 
memory can be allocated. This is common when compiling template-heavy 
code.

ii) the fast vector units do not help anything for compiling the code.

iii) the optimizer is very aggressive, checking every piece of code for 
vectorization and parallelization possibilities, which makes it even 
slower. I don't think your PC compiler does that.

And finally, it actually only takes about 10 minutes to compile :)

Matthias