Den 01/05/2012 kl. 15.55 skrev Gary Palmer:
>
> If you want a high-level view of what goes on run
>
> ldd `which ls`
>
> check that it has libraries to load and doesn't say "not a dynamic ELF
> executable", and then run:
>
> ktrace ls
> kdump | more
>
> All the system calls related to resolving and loading shared libraries
> take time. I realise "ls" is not "make", but it should give you an
> idea.
Just for fun, I did some measurements with ktrace and a static vs dynamic make.
I did 'ktrace make' and 'trace dynamicmake' ('dynamicmake' produced by running
'make NO_SHARED=no' in /usr/src/usr.bin/make), just to see where time is spent
when loading and running make in the static and dynamic cases. I did this 100
times for each version (discarding the first run) and ran through ministat
(numbers in msecs):
x static.dat
+--------------------------------------------------------------------------------+
| x x
|
| x x x x x x x
|
| x x x x x x x x
|
| x x x x x x x x x x x x x
|
| x x x x x x x x x x x x x x x x x
|
| x x x x x x x x x x x x x x x x x x x x x x x
|
|x x x x x x x x x x x x x x x x x x x x x x x x x x x x x
x|
| |_____________M__A_______________|
|
+--------------------------------------------------------------------------------+
N Min Max Median Avg Stddev
x 100 2.228 2.266 2.242 2.24333 0.00794
x dynamic.dat
+--------------------------------------------------------------------------------+
| x
|
| xx
|
| x xx x x x
|
| x xx x x xx x
|
| x x xx x x xx x x x
|
| x x x x x xx x x xx x x x x
|
|x x x xx x x x xx x x x x xx x x x x x x
|
|x xx x x x xx x x x xx x x x x xx x x x x xx x x x x xx x x x
x|
| |_____________M_A_______________|
|
+--------------------------------------------------------------------------------+
N Min Max Median Avg Stddev
x 100 2.648 2.691 2.666 2.6669 0.00873
So the dynamic version is ca. 0.42 ms, or 16%, slower on my system.
I then compared a trace from a static and a dynamic 'make'. Both selected
traces had a running time matching the median of that run. I cut away all
common system calls etc., which resulted in just the steps involved in loading
'make' to a state where it can start executing.
In the static case, this took 0.26 ms. In the dynamic case, this took 0.57 ms,
or 0.31 ms (119%) more. The remaining ca. 0.11 ms (0.42 - 0.31) are mainly due
to the dynamic version having slightly slower IO (read() and stat()). I have no
idea why. The following are the notable steps in each version:
Static version:
* 0.09 ms spent execve'ing /usr/bin/make
* The rest is mostly sysctl calls
Dynamic version:
* 0.09 ms spent execve'ing ./dynamicmake and /libexec/ld-elf.so.1
* 0.18 ms spent loading libc.so.7 (incl. reading /etc/libmap.conf and
/var/run/ld-elf.so.hints)
* 0.11 ms spent calling sysarch(0x81,0x7fffffffXXXX) (static version also does
this but only uses 0.01 ms. No idea why)
* The rest is mostly sysctl and sigprocmask calls
Loading of libc.so.7 does indeed seem to be the main culprit.
Thanks,
Erik_______________________________________________
freebsd-current@freebsd.org mailing list
http://lists.freebsd.org/mailman/listinfo/freebsd-current
To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
