g++ spent lots of user time

[w***@totalbb.net.tw]

Why did the compilation took so long in user time?

-----------------
$g++ --version
g++ (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1)
...

$time g++ -c -Wall -pthread -fPIC dsmain.cpp

real 6m10.623s
user 6m8.142s
sys 0m0.099s

[Lew Pitcher]

On Wednesday March 1 2017 09:05, in comp.os.linux.development.apps,
"***@totalbb.net.tw" <***@totalbb.net.tw> wrote:

[Text order altered]

Post by w***@totalbb.net.tw
-----------------
$g++ --version
g++ (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1)
...
$time g++ -c -Wall -pthread -fPIC dsmain.cpp
real 6m10.623s
user 6m8.142s
sys 0m0.099s
Why did the compilation took so long in user time?

You have not provided enough information to allow anyone to give you a
comprehensive answer to your question.

I can give you a generic answer to your question, though.

Your compilation tool a long time because the compiler was doing lots of
complicated things that didn't require any system calls.

Process time is split into "the length of time the process waited while the OS
serviced a process-initiated system call, such as open() or read()" and "the
rest of the time that the process took to execute". Your "system call time"
(or "sys") is 0 minutes, 0.099 seconds, while your "everything else time" (or
"user") is 6 minutes, 8.142 seconds. That's all we can tell from the
information you supplied.

[w***@totalbb.net.tw]

Post by Lew Pitcher
On Wednesday March 1 2017 09:05, in comp.os.linux.development.apps,
[Text order altered]

Post by w***@totalbb.net.tw
-----------------
$g++ --version
g++ (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1)
...
$time g++ -c -Wall -pthread -fPIC dsmain.cpp
real 6m10.623s
user 6m8.142s
sys 0m0.099s
Why did the compilation took so long in user time?

You have not provided enough information to allow anyone to give you a
comprehensive answer to your question.
I can give you a generic answer to your question, though.
Your compilation tool a long time because the compiler was doing lots of
complicated things that didn't require any system calls.
Process time is split into "the length of time the process waited while the OS
serviced a process-initiated system call, such as open() or read()" and "the
rest of the time that the process took to execute". Your "system call time"
(or "sys") is 0 minutes, 0.099 seconds, while your "everything else time" (or
"user") is 6 minutes, 8.142 seconds. That's all we can tell from the
information you supplied.
--
Lew Pitcher
"In Skills, We Trust"
PGP public key available upon request

The lack of information is intentional, because it has never occurred at least
4 month before for more than 10 years, it might involve template things though.
But it contains about 1500 lines, it is not shown.
Currently, almost every object files in the Makefile takes nearly 10 more
minutes to compile. So I think it should be mostly the 'feature' of newer g++

[Rainer Weikusat]

[...]

Post by w***@totalbb.net.tw

Post by Lew Pitcher

Post by w***@totalbb.net.tw
-----------------
$g++ --version
g++ (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1)
...
$time g++ -c -Wall -pthread -fPIC dsmain.cpp
real 6m10.623s
user 6m8.142s
sys 0m0.099s
Why did the compilation took so long in user time?

[...]

Post by w***@totalbb.net.tw

Post by Lew Pitcher
Your compilation tool a long time because the compiler was doing lots of
complicated things that didn't require any system calls.

[...]

Post by w***@totalbb.net.tw
Currently, almost every object files in the Makefile takes nearly 10 more
minutes to compile. So I think it should be mostly the 'feature' of newer g++

This strongly suggests that you're keeping the compiler busy with doing
and re-doing loads of avoidable things. Considering that this is C++,
that's almost certainly template-related.

It should be possible to detemine the exact cause using #if 0
... #endif to neutralize all of the code in this file and than
re-activate it bit by bit until the problematic part has been found.

[Johann Klammer]

Post by w***@totalbb.net.tw
Why did the compilation took so long in user time?
-----------------
$g++ --version
g++ (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1)
...
$time g++ -c -Wall -pthread -fPIC dsmain.cpp
real 6m10.623s
user 6m8.142s
sys 0m0.099s

That's g++. especially their C++ compiler is awfully slow.
Not sure what it is. maybe the parser... those STL headers
with all the templates. or their garbage collector. I
suspect it's not very good at collecting the garbage...
Maybe it is time to look for alternatives.

[w***@totalbb.net.tw]

Post by Johann Klammer

Post by w***@totalbb.net.tw
Why did the compilation took so long in user time?
-----------------
$g++ --version
g++ (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1)
...
$time g++ -c -Wall -pthread -fPIC dsmain.cpp
real 6m10.623s
user 6m8.142s
sys 0m0.099s

That's g++. especially their C++ compiler is awfully slow.
Not sure what it is. maybe the parser... those STL headers
with all the templates. or their garbage collector. I
suspect it's not very good at collecting the garbage...
Maybe it is time to look for alternatives.

I don't use STL, and even the standard library. But I do
start learning another language instead following C++'s many
new things, making codes difficult to comprehend and maintain.