Performance degradation with ROOT 20.04 & 22.6

[janmayer]

With ROOT 20.04, the performance of the GUI window is slow, especially over ssh.

Workaround: Use ROOT 18.04.
This requires
include(${ROOT_DIR}/modules/RootNewMacros.cmake)
instead of
include(${ROOT_DIR}/RootMacros.cmake)
in the three CMakeLists.

[janmayer]

The problem persists in ROOT 6.22.6

[janmayer]

I think I have identified the commit in ROOT that causes the issue.

Procedure: I started with the knowledge that 6.18.04 was working and 6.20.00 was not. Unfortunately, the branch v6-18-00-patches and the associated tags are not properly connected to the 6.20. branch. However, through some trial and error I found that tag v6-19-01 was good and v6-19-02 was bad. (Both versions are unreleased.)

Through bisecting I found:

git bisect start
git checkout v6-19-01
git bisect good
git checkout v6-19-02
git bisect bad
f15b9502503786c79236f860d16d36e6351f5b1d -> bad
36c9ed2d7c37102ed8791d0c139e8852e98e84bf -> bad
805d118461d18d3a9fa0285099ccf3d197101c7b -> bad
93312a27e24049d9717071e2df7f355b5299915f -> good
340d6aa621557aa0a5ae7878f0440db8435827c6 -> good
1b0fd63245a614fe9ff9ee228b7be8e84cc14100 -> good
9132e16fab9fe680658c1438d6ff98358dda9b76 -> bad
42ef9790c9d90394880dd60425700e92c56292cf -> good
75161283352217c156c435ba8bac870cd5a125fb -> bad
5e87e28b84c0ecc2d41bfc8d01f844312c0c1809 -> good
01bd9140ec9a9abc5f28acf0a64cf77c975c9408 -> good

75161283352217c156c435ba8bac870cd5a125fb is the first bad commit
commit 75161283352217c156c435ba8bac870cd5a125fb
Author: Bertrand Bellenot <[email protected]>
Date:   Mon Jun 24 13:22:25 2019 +0200

    Set `X11.UseXft` to `yes` by default

I.e. this miniscule change seems to have caused the performance degradation. A fix for that should be possible to find on our side.

Note that while bisecting, I ended up with this compile script to avoid strange errors and reduce compilation time. Full recompilation every time to avoid other strange errors.

rm -rf install
rm -rf build
mkdir build
cd build

cmake /scratch/jmayer/root \
        -DCMAKE_INSTALL_PREFIX=/scratch/jmayer/install \
        -Dcxx11=ON \
        -Dpython=ON \
        -DPYTHON_EXECUTABLE=/opt/rh/rh-python38/root/usr/bin/python \
        -DCMAKE_BUILD_TYPE=Debug \
        -Ddavix=OFF \
        -Dbuiltin_davix=OFF \
        -DLLVM_TARGETS_TO_BUILD="host;NVPTX" \
        -Dtvma=OFF \
        -Droofit=OFF \
        -Dxrootd=OFF \
        -Dclad=OFF \
        -Dcudnn=OFF \
        -Ddataframe=OFF \
        -Dgdml=OFF \
        -Dgfal=OFF \
        -Dmlp=OFF \
        -Doracle=OFF \
        -Dpgsql=OFF \
        -Dpythia6=OFF \
        -Dpythia8=OFF \
        -Dsqlite=OFF \
        -Dvdt=OFF \
        -Dbuiltin_glew=ON
nice make -j30
nice make install -j30

It might be an idea to find the minimal ROOT build configuration in order to run hdtv.

[janmayer]

Solution is ROOT.gEnv.SetValue("X11.UseXft", 0).