Date: Wed, 2 May 2012 00:46:04 +0200 From: Erik Cederstrand <erik@cederstrand.dk> To: Gary Palmer <gpalmer@freebsd.org> Cc: freebsd-current FreeBSD <freebsd-current@freebsd.org> Subject: Re: [RFC] Un-staticise the toolchain Message-ID: <13119BE4-531E-4681-89F0-876DC272B18F@cederstrand.dk> In-Reply-To: <20120501135530.GA50127@in-addr.com> References: <20120426093548.GR2358@deviant.kiev.zoral.com.ua> <20120426134140.GF14350@lo0.su> <CADLo838sdUT2e%2B7j8vCyOmDithLsh3kwDd_z04dWaPoiMphPDQ@mail.gmail.com> <4F99ACF9.2050609@infracaninophile.co.uk> <CADLo83_sr=13H=9nnrdge0jJaOh5Bk2N_gg=Gf-uYhwM8jm7Xg@mail.gmail.com> <42D8809D-0E99-47A5-802F-71991B5B0B8D@cederstrand.dk> <A79EE48D-A2AC-4D35-B156-1F58D17F77DD@kientzle.com> <AF37B4BF-69D5-41D3-819A-0252911CBC89@cederstrand.dk> <20120501135530.GA50127@in-addr.com>
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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
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