Today I've read (twice) that the overhead of frame pointers on the
runtime of the compiler, GCC, is 10%. This number is nonsense. The
actual overhead is 1%, and I have done the tests that show this.
I want to note up front that it was also claimed that GCC slowed down
by 10% between Fedora 37 & 38 (when frame pointers were introduced).
However frame pointers have been disabled in our GCC build on all
architectures for 9 months, since before Fedora 38 was released. So
if there has been such a slowdown (which I don't know) then it cannot
be anything to do with frame pointers. At the same time GCC was
upgraded from 12 to 13, such a signicant new release that claims
comparing versions of Fedora are not valid.
- - -
In my tests I recompiled GCC with frame pointers enabled (see
gcc-add-fp.patch), and then built qemu with 'make clean; time make -j32'.
I took the 'user' time over 3 runs. The average user time was 1135
seconds.
I then recompiled binutils with frame pointers disabled (see
binutils-no-fp.patch), and installed it alongside
gcc-13.2.1-4.fc40.x86_64 (which as noted above has frame pointers
disabled). The average user time over 3 runs was 1122 seconds.
With frame pointers: 1135 seconds
Without frame pointers: 1122 seconds
Overhead: 1.01%
Note also that the wallclock time in every case was either 41 or 42
seconds, so in practical terms for users there is no difference with
or without frame pointers.
You may also note that I didn't recompile any libraries (so in my
tests, frame pointers are used in both cases). However using
profiling we can show that this doesn't matter. The total time used
during the make -j32 run by each binary and DSO was:
58.41% lto1
14.97% cc1
11.47% Linux kernel
7.68% libc.so.6
4.31% as
1.54% libbfd-2.41-7.fc40.so
0.64% libpython3.12.so.1.0
0.26% ld-linux-x86-64.so.2
0.09% ld.bfd
0.00% python3.12
(everything else under 1%)
Note the only library which consumes any significant time is libc, but
at under 8% it would hardly affect the test times. libbfd is actually
part of binutils so it was recompiled with & without frame pointers.
Full raw results are in the attached file.
Rich.
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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Q: How much are libraries used?
Children Self Shared Object
+ 97.79% 7.68% libc.so.6 ◆
+ 65.25% 58.41% lto1 ▒
+ 20.62% 14.97% cc1 ▒
+ 12.33% 11.47% [kernel.kallsyms] ▒
+ 8.08% 4.31% as ▒
+ 6.03% 1.54% libbfd-2.41-7.fc40.so ▒
+ 1.88% 0.09% ld.bfd ▒
+ 0.79% 0.64% libpython3.12.so.1.0 ▒
+ 0.78% 0.00% python3.12 ▒
+ 0.67% 0.26% ld-linux-x86-64.so.2 ▒
build qemu 'make -j32' (2591 targets)
gcc-13.2.1-4.fc40.x86_64 (FP accidentally turned off)
real 0m41.297s
user 18m38.587s
sys 2m5.460s
real 0m41.218s
user 18m36.044s
sys 2m3.838s
real 0m41.493s
user 18m42.651s
sys 2m4.668s
above + binutils-2.41-8.1.nofp.fc40.x86_64 (FP turned off)
real 0m41.357s
user 18m39.692s
sys 2m4.310s
real 0m41.403s
user 18m43.905s
sys 2m4.399s
real 0m41.389s
user 18m44.637s
sys 2m4.407s
Average user: 1122
binutils-2.41-7.fc40.x86_64 + gcc-13.2.1-4.1.fp.fc40.x86_64 (FP turned on)
real 0m41.702s
user 18m51.091s
sys 2m3.045s
real 0m42.000s
user 18m56.555s
sys 2m3.301s
real 0m42.029s
user 18m58.724s
sys 2m3.922s
Average user: 1135
Overhead of frame pointers: 1135/1122 = 1.01%
diff --git a/gcc.spec b/gcc.spec
index 5d6c7c4..c7774fd 100644
--- a/gcc.spec
+++ b/gcc.spec
@@ -136,7 +136,7 @@
Summary: Various compilers (C, C++, Objective-C, ...)
Name: gcc
Version: %{gcc_version}
-Release: %{gcc_release}%{?dist}
+Release: %{gcc_release}.1.fp%{?dist}
# libgcc, libgfortran, libgomp, libstdc++ and crtstuff have
# GCC Runtime Exception.
License: GPLv3+ and GPLv3+ with exceptions and GPLv2+ with exceptions and LGPLv2+ and BSD
@@ -923,7 +923,6 @@ OPT_FLAGS=`echo $OPT_FLAGS|sed -e 's/-flto=auto//g;s/-flto//g;s/-ffat-lto-object
OPT_FLAGS=`echo $OPT_FLAGS|sed -e 's/-m64//g;s/-m32//g;s/-m31//g'`
OPT_FLAGS=`echo $OPT_FLAGS|sed -e 's/-mfpmath=sse/-mfpmath=sse -msse2/g'`
OPT_FLAGS=`echo $OPT_FLAGS|sed -e 's/ -pipe / /g'`
-OPT_FLAGS=`echo $OPT_FLAGS|sed -e 's/-fno-omit-frame-pointer//g;s/-mbackchain//g;s/-mno-omit-leaf-frame-pointer//g'`
OPT_FLAGS=`echo $OPT_FLAGS|sed -e 's/-Werror=format-security/-Wformat-security/g'`
%ifarch sparc
OPT_FLAGS=`echo $OPT_FLAGS|sed -e 's/-mcpu=ultrasparc/-mtune=ultrasparc/g;s/-mcpu=v[78]//g'`
diff --git a/binutils.spec b/binutils.spec
index 472338a..d92c907 100644
--- a/binutils.spec
+++ b/binutils.spec
@@ -1,8 +1,9 @@
+%undefine _include_frame_pointers
Summary: A GNU collection of binary utilities
Name: binutils%{?_with_debug:-debug}
Version: 2.41
-Release: 8%{?dist}
+Release: 8.1.nofp%{?dist}
License: GPL-3.0-or-later AND (GPL-3.0-or-later WITH Bison-exception-2.2) AND (LGPL-2.0-or-later WITH GCC-exception-2.0) AND BSD-3-Clause AND GFDL-1.3-or-later AND GPL-2.0-or-later LGPL-2.1-or-later AND LGPL-2.0-or-later
URL: https://sourceware.org/binutils
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