[Qt-interest] Performance problem with Qt4.6.2 and QString on lucid ubuntu

[Abdelrazak Younes]

On 03/18/2010 05:59 PM, Abdelrazak Younes wrote:
> Hello,
>
> With Qt4.6.2 my application sudenly rquires a lot of CPU under Linux 
> (about 40% cpu, compiled with gcc-4.4 ubuntu lucid). A quick oprofile 
> reveals that most of the time is in QBasicAtomicInt::deref() and 
> QString::~QString().
>
> The same application compiled with MSVC-2008 on Windows takes 
> basically no-cpu (less than 1%).
> The same application compiled with Qt4.5.2 on a Debian system doesn't 
> have this problem either...
>
> In my application I do a lot of data passing from the core to the gui 
> using QStrings and QStringList. Either by copy and using const reference.
>

Just in case someone has an idea, here is the oprofile:


CPU: Core 2, speed 1992 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a 
unit mask of 0x00 (Unhalted core cycles) count 100000
samples  %        image name               app name                 
symbol name
-------------------------------------------------------------------------------
224877   60.3062  libQtCore.so.4.6.2       SoftPlug                 
/usr/lib/libQtCore.so.4.6.2
   224877   100.000  libQtCore.so.4.6.2       SoftPlug                 
/usr/lib/libQtCore.so.4.6.2 [self]
-------------------------------------------------------------------------------
27198     7.2938  libc-2.11.1.so           SoftPlug                 malloc
   27198    100.000  libc-2.11.1.so           SoftPlug                 
malloc [self]
-------------------------------------------------------------------------------
24342     6.5279  libc-2.11.1.so           SoftPlug                 free
   24342    100.000  libc-2.11.1.so           SoftPlug                 
free [self]
-------------------------------------------------------------------------------
13646     3.6595  libc-2.11.1.so           SoftPlug                 memcpy
   13646    100.000  libc-2.11.1.so           SoftPlug                 
memcpy [self]
-------------------------------------------------------------------------------
11153     2.9909  libc-2.11.1.so           SoftPlug                 
_int_malloc
   11153    100.000  libc-2.11.1.so           SoftPlug                 
_int_malloc [self]
-------------------------------------------------------------------------------
8271      2.2181  libc-2.11.1.so           SoftPlug                 
_int_free
   8271     100.000  libc-2.11.1.so           SoftPlug                 
_int_free [self]
-------------------------------------------------------------------------------
5938      1.5924  libc-2.11.1.so           oprofiled                vfprintf
   5938     100.000  libc-2.11.1.so           oprofiled                
vfprintf [self]
-------------------------------------------------------------------------------
4420      1.1853  SoftPlug                 SoftPlug                 
QBasicAtomicInt::deref()
   4420     100.000  SoftPlug                 SoftPlug                 
QBasicAtomicInt::deref() [self]
-------------------------------------------------------------------------------
3337      0.8949  libc-2.11.1.so           oprofiled                
_IO_file_xsputn@@GLIBC_2.2.5
   3337     100.000  libc-2.11.1.so           oprofiled                
_IO_file_xsputn@@GLIBC_2.2.5 [self]
-------------------------------------------------------------------------------
2947      0.7903  Xorg                     Xorg                     
/usr/bin/Xorg
   2947     100.000  Xorg                     Xorg                     
/usr/bin/Xorg [self]
-------------------------------------------------------------------------------
2914      0.7815  r300_dri.so              Xorg                     
/usr/lib/dri/r300_dri.so
   2914     100.000  r300_dri.so              Xorg                     
/usr/lib/dri/r300_dri.so [self]
-------------------------------------------------------------------------------
2528      0.6779  libc-2.11.1.so           SoftPlug                 
malloc_consolidate
   2528     100.000  libc-2.11.1.so           SoftPlug                 
malloc_consolidate [self]
-------------------------------------------------------------------------------
2504      0.6715  libQtGui.so.4.6.2        SoftPlug                 
/usr/lib/libQtGui.so.4.6.2
   2504     100.000  libQtGui.so.4.6.2        SoftPlug                 
/usr/lib/libQtGui.so.4.6.2 [self]
-------------------------------------------------------------------------------
2213      0.5935  SoftPlug                 SoftPlug                 
QString::~QString()
   2213     100.000  SoftPlug                 SoftPlug                 
QString::~QString() [self]
-------------------------------------------------------------------------------
1614      0.4328  libpixman-1.so.0.16.4    Xorg                     
/usr/lib/libpixman-1.so.0.16.4
   1614     100.000  libpixman-1.so.0.16.4    Xorg                     
/usr/lib/libpixman-1.so.0.16.4 [self]
-------------------------------------------------------------------------------
1451      0.3891  oprofiled                oprofiled                
/usr/bin/oprofiled
   1451     100.000  oprofiled                oprofiled                
/usr/bin/oprofiled [self]
-------------------------------------------------------------------------------
1435      0.3848  SoftPlug                 SoftPlug                 
QList<QString>::node_destruct(QList<QString>::Node*, QList<
QString>::Node*)