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

From: David Abrahams (dave_at_[hidden])
Date: 2003-01-18 16:33:25

Matthias Troyer <troyer_at_[hidden]> writes:

> 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.

Just one question: why the heck don't they make a cross-compiler which
runs on a machine better-suited to compilation?

> 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.

There's no reason it couldn't, though.

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

Utterly painless! ;-)

-- 
                       David Abrahams
   dave_at_[hidden] * http://www.boost-consulting.com
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