One of my biggest annoyances with NixOS on desktop these days is that apps are too darn slow to start. Not 2 seconds slow (that would be unusable), but ballpark of 0.5 seconds slow, between me hitting Enter to open an App, and GUI actually showing up. So I am on a make-shift crusade to fix it file & follow the relevant issues. And plasma-emojier is my trusty companion.
In Episode I, it was discovered that the bash script wrapping emojier is accidentally quadratic. As they say, optimize big-O first, so we swapped in C for bash to get some decent improvement.
In Episode II, a discrepancy was observed between starting emojier from the CLI and using a global shortcut. This was due to some extra unnecessary intermediate process on the Plasma side, which was since fixed in Port app launching to ApplicationLauncherJob (!3) · Merge requests · Plasma / KGlobalAccel Daemon · GitLab.
In Episode III, I got significant cold start speed up by disabling my nvidia GPU. I used nixos-hardware to turn it off, and nvtop to confirm that it is, in fact, turned off. Which wasn’t enough — I also had to completely remove hardware.nvidia, otherwise the emojier tried to poke the device with disastrous (for start up times) consequences:
openat(AT_FDCWD, "/sys/bus/pci/devices/0000:00:0d.0/config", O_RDONLY) = 15 <0.000014>
read(15, "\206\200\36F\6\4\220\2\0020\3\f\20\0\200\0\4\0&\5b\0\0\0\0\0\0\0\0\0\0\0"..., 48) = 48 <0.173553>
openat(AT_FDCWD, "/sys/bus/pci/devices/0000:00:01.0/config", O_RDONLY) = 15 <0.000090>
read(15, "\206\200\rF\7\5\20\0\2\0\4\6\20\0\201\0\0\0\0\0\0\0\0\0\0\1\1\0@@\0 "..., 48) = 48 <0.165022>
Now, the above is probably a bug — my dGPU is powered off, and all the rendering is done by intel. There’s no reason software should be poking at that pci bus at all. I haven’t filed a bug about that, as I have no idea which layer of software stack is responsible for doing those reads 
But, anyway, completely jettisoning nvidia worked for me 
So now we come to Episode IV, this installment.
Emojier is … well, it isn’t drunken slug slow anymore:
λ t plasma-emojier --version
plasma.emojier 5.27.10
real 191.44ms
cpu 179.92ms (130.39ms user + 49.53ms sys)
rss 101.17mb
But fast this clearly isn’t.
Here’s what strace has to say about this:
λ strace -w -c plasma-emojier --version
plasma.emojier 5.27.10
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- -------------------
60.64 0.145800 9 14865 14096 statx
6.61 0.015888 9 1640 1549 readlink
5.90 0.014175 11 1240 923 openat
5.32 0.012794 17 743 mmap
I think this is us, NixOS. We have some ridiculously long search paths which emojier tries in order to load some things:
newfstatat(AT_FDCWD, "/nix/store/ga17mlfsss2fndyvp2s1m0s2rx2b4i9s-libX11-1.8.7/lib/", {st_mode=S_IFDIR|0555, st_size=4096, ...}, 0) = 0 <0.000010>
openat(AT_FDCWD, "/nix/store/znk677nrcipl9jrnwjfzfx65wdmh77iy-qtbase-5.15.12/lib/glibc-hwcaps/x86-64-v3/libKF5ConfigGui.so.5", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory) <0.000011>
newfstatat(AT_FDCWD, "/nix/store/znk677nrcipl9jrnwjfzfx65wdmh77iy-qtbase-5.15.12/lib/glibc-hwcaps/x86-64-v3/", 0x7ffe3d51b190, 0) = -1 ENOENT (No such file or directory) <0.000009>
openat(AT_FDCWD, "/nix/store/znk677nrcipl9jrnwjfzfx65wdmh77iy-qtbase-5.15.12/lib/glibc-hwcaps/x86-64-v2/libKF5ConfigGui.so.5", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory) <0.000010>
newfstatat(AT_FDCWD, "/nix/store/znk677nrcipl9jrnwjfzfx65wdmh77iy-qtbase-5.15.12/lib/glibc-hwcaps/x86-64-v2/", 0x7ffe3d51b190, 0) = -1 ENOENT (No such file or directory) <0.000009>
openat(AT_FDCWD, "/nix/store/znk677nrcipl9jrnwjfzfx65wdmh77iy-qtbase-5.15.12/lib/libKF5ConfigGui.so.5", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory) <0.000010>
newfstatat(AT_FDCWD, "/nix/store/znk677nrcipl9jrnwjfzfx65wdmh77iy-qtbase-5.15.12/lib/", {st_mode=S_IFDIR|0555, st_size=12288, ...}, 0) = 0 <0.000010>
openat(AT_FDCWD, "/nix/store/56rvf22j5bn7jpmbmd2ia88mkxpfc8pm-ki18n-5.114.0/lib/glibc-hwcaps/x86-64-v3/libKF5ConfigGui.so.5", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory) <0.000010>
newfstatat(AT_FDCWD, "/nix/store/56rvf22j5bn7jpmbmd2ia88mkxpfc8pm-ki18n-5.114.0/lib/glibc-hwcaps/x86-64-v3/", 0x7ffe3d51b190, 0) = -1 ENOENT (No such file or directory) <0.000009>
openat(AT_FDCWD, "/nix/store/56rvf22j5bn7jpmbmd2ia88mkxpfc8pm-ki18n-5.114.0/lib/glibc-hwcaps/x86-64-v2/libKF5ConfigGui.so.5", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory) <0.000009>
... and a thousand futile attempts more like this ...
Is there anything we can do here? Or perhaps there’s something KDE folks can do to make NixOS and plasma play nicer together?