Re: Suggested method for returning a string from a C program?

On 28/03/2025 20:41, Scott Lurndal wrote:

bart <bc@freeuk.com> writes:

On 28/03/2025 16:13, Scott Lurndal wrote:

Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

scott@slp53.sl.home (Scott Lurndal) writes:
>

[...]  I have one
source file that takes almost 7 minutes to compile
when using -O3 on a very-high-end xeon box.  Mostly
buried in the overall compile time when using parallel
make.
>
The code could be restructured to compile in a few seconds;
but that would require substantial changes to the rest
of the codebase.   Compiling with -O0 for development
testing reduces the compile time to a few seconds.

>
How long does it take compiling with -O1?

>
Using -O1 saves 14 seconds on the long-pole.
>
>
$ time mr -s -j96
   COMPILE g.cpp
   BUILD lib/lib_g.so
   BUILDSO libsim.so.1.0
   BUILD TARGET sim
>
real    14m0.76s
user    13m52.28s
sys     0m20.13s
>
$ time md -s -j96
   COMPILE g.cpp
   BUILD lib_g.so
   BUILDSO libsim.so.1.0
   BUILD TARGET sim
>
real    13m46.49s
user    13m42.17s
sys     0m16.66s
>
To be clear, we know that this is ridiculous, the generated
header file totals 1.25 million lines, including a single
function with over 200,000 SLOC.   Feature creep, antique
algorithms, screwed up third-party ip-xact collateral and
tight development schedules.

>
So, 13:40 minutes for 1.25M lines? (I assume that header contains code
not just declarations.)
>
That would make it 1.5Kloc/second, but it also apparently over 96 cores
(or threads)? That comes to 16 lines per second per thread.

 The gnu compiler is not multithreaded.  The single thread was
compute bound for 13 minutes and 46 seconds.

So what was that -j96 about?

 

>
That 200K lines in one function looks suspicious

 Why?

I thought I explained. Compile-time for a long function can increase non-linearly in a complex compiler. It could also use up more memory than the same line-count but split into separate functions.