New subject: [Bug 859561] Executable's speed jumping between low and high in some computers

21 Jan 2014

      https://bugzilla.novell.com/show_bug.cgi?id=859561

https://bugzilla.novell.com/show_bug.cgi?id=859561#c0

           Summary: Executable's speed jumping between low and high in
                    some computers
    Classification: openSUSE
           Product: openSUSE 13.1
           Version: Final
          Platform: x86-64
        OS/Version: openSUSE 13.1
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: Kernel
        AssignedTo: kernel-maintainers@forge.provo.novell.com
        ReportedBy: j9002j@yahoo.com
         QAContact: qa-bugs@suse.de
          Found By: ---
           Blocker: ---

User-Agent:       Mozilla/5.0 (X11; Linux x86_64; rv:26.0) Gecko/20100101
Firefox/26.0

A compiled (locally on or another computer) executable runs at different speeds
in the same computer. 

Sometimes the behavior is bistable: the executable runs at definite slow or
definite high speeds. In a looping program, the speed can change during the
looping.

At first, another problem with libm was suspected, but a simple program written
not to use that library shows bistable behavior.

The computer is not otherwise loaded.

This phenomenon was not observed with previous versions of opensuse.

In one computer, the bistable behavior was observed right after installation in
December 2013, and almost vanished after a few updates. On another computer, it
still persists. The difference in speeds is 2-3 times. The loaded core's
frequency stays at highest possible during executable (besides when the
microcode update package is removed; see below).

Reproducible: Sometimes

Steps to Reproduce:
1. Boot a x86-64 computer. Let it run the usual tasks for a few hours or more.

2. Compile and run a simple looping program in C++ doing math calculations,
with or without usage of math functions in libm. Observe the execution speed.
The compilation command does not matter, but could be 
g++ -Wall -O2 mycode.C  An example program is below:

//---------------------------------------------------------------------------
# include <iostream>
# include 

//---------------------------------------------------------------------------
static const volatile double COS2PI5  =  0.30901699437494745;
static const volatile double SIN2PI5  =  0.95105651629515353;
static const volatile double COS4PI5  = -0.80901699437494734;
static const volatile double SIN4PI5  =  0.58778525229247325;

//---------------------------------------------------------------------------
using namespace std;

//---------------------------------------------------------------------------
void fft5(double* ro, double* io, double* ri, double* ii);

//---------------------------------------------------------------------------
int main(int argc, char* argv[])
{
int i, j, n, N, M;
M = 50;
N = 50000000;
n = 5;
clock_t t0, t1;

double* ri = new double[n];
double* ii = new double[n];
double* ro = new double[n];
double* io = new double[n];

for (i = 0; ihttps://forums.opensuse.org/showthread.php/494420-Executable-s-speed-jumping...

The BIOS versions on computers are the latest ones. memtest shows no errors.

The removal of package ucode-intel has no clear effect on the bistable
behavior. Same when the package is replaced with older versions of microcode
update package. The microcode package may have some influence on CPU frequency.

An incomplete investigation shows the bistable behavior with one of the next
versions of the kernel (the version number is not preserved).

On some computers the bistable speed is not reproducible. On some, it is
difficult to reproduce. On some, it is difficult to avoid. Conditions favoring
bistable behavior are shutdowns with power-off, reboots, software updates.

================= The kernel and compiler used ================
...
uname -a
Linux computer 3.11.6-4-desktop #1 SMP PREEMPT Wed Oct 30 18:04:56 UTC 2013
(e6d4a27) x86_64 x86_64 x86_64 GNU/Linux
...
gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib64/gcc/x86_64-suse-linux/4.8/lto-wrapper
Target: x86_64-suse-linux
Configured with: ../configure --prefix=/usr --infodir=/usr/share/info
--mandir=/usr/share/man --libdir=/usr/lib64 --libexecdir=/usr/lib64
--enable-languages=c,c++,objc,fortran,obj-c++,java,ada
--enable-checking=release --with-gxx-include-dir=/usr/include/c++/4.8
--enable-ssp --disable-libssp --disable-plugin
--with-bugurl=http://bugs.opensuse.org/ --with-pkgversion='SUSE Linux'
--disable-libgcj --disable-libmudflap --with-slibdir=/lib64 --with-system-zlib
--enable-__cxa_atexit --enable-libstdcxx-allocator=new --disable-libstdcxx-pch
--enable-version-specific-runtime-libs --enable-linker-build-id
--program-suffix=-4.8 --enable-linux-futex --without-system-libunwind
--with-arch-32=i586 --with-tune=generic --build=x86_64-suse-linux
Thread model: posix
gcc version 4.8.1 20130909 [gcc-4_8-branch revision 202388] (SUSE Linux)
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[Bug 859561] New: Executable's speed jumping between low and high in some computers

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