Checking special execution durations for the determination of mountable file systems

[Markus Elfring <Markus.Elfring@web.de>]

Hello,

I came along the need to check unexpected software execution durations
at another place.

* Qt
   https://doc.qt.io/qt-5/qstorageinfo.html#mountedVolumes

* KPMcore
   https://github.com/KDE/kpmcore/blob/ce39e149040bce9782b91e532d041ca0c7548a77/src/fs/filesystem.cpp#L145

Example:
[Markus_Elfring@fedora mountedVolumes]$ time ./mountedVolumes
Number of eventually mounted filesystems: 43

real    3m3,561s
user    0m0,016s
sys    0m0,026s


I increased software analysis efforts accordingly.
https://github.com/namhyung/uftrace/

[Markus_Elfring@fedora mountedVolumes]$ time sudo uftrace record --data=/home/Markus_Elfring/Test/mountedVolumes/Probe-uftrace/ --nest-libcall --kernel --num-thread=4 ./mountedVolumes
Number of eventually mounted filesystems: 42

real    3m4,835s
user    0m0,346s
sys    0m3,549s


[Markus_Elfring@fedora ~]$ uftrace --data=Test/mountedVolumes/Probe-uftrace report --filter=QStorageInfo::mountedVolumes
   Total time   Self time       Calls  Function
   ==========  ==========  ==========  ====================
     3.000  m  478.403 us           1  QStorageInfo::mountedVolumes
     3.000  m   38.261 us          90  QStorageInfo::QStorageInfo
     3.000  m   10.244 ms          48  QStorageInfo::setPath
     3.000  m    3.000  m          23  linux:schedule
     3.000  m    1.030  m          48  statvfs64
     1.030  m    1.315 ms          47  __x64_sys_statfs
    45.887 ms    5.746 ms         944  QDirIterator::next
    28.768 ms    3.691 ms         944  QFileInfo::symLinkTarget
    19.421 ms    1.246 ms        3185  fgets
    18.845 ms  659.323 us        1900  QFileInfo::isFile
    18.035 ms    1.207 ms         950  statx
…


Another bit of background information:
The function “statvfs64” gets called by the function “QStorageInfoPrivate::retrieveVolumeInfo” (which is called by the function “QStorageInfoPrivate::doStat” and so on).
https://github.com/bminor/glibc/blob/595c22ecd8e87a27fd19270ed30fdbae9ad25426/sysdeps/unix/sysv/linux/statvfs64.c#L27
https://code.woboq.org/qt5/qtbase/src/corelib/io/qstorageinfo_unix.cpp.html#_ZN19QStorageInfoPrivate18retrieveVolumeInfoEv
https://code.woboq.org/qt5/qtbase/src/corelib/io/qstorageinfo_unix.cpp.html#_ZN19QStorageInfoPrivate14mountedVolumesEv


Would you like to help with the clarification for the shown measurements?

Regards,
Markus