performance improvements

- improve initialization performance by caching the selected runtime and thereby skipping the slow automatic runtime selection
- print initialization duration when NP_DEBUG is set
- adjust compression levels for nix-portable release to achieve a smaller file size

default.nix

@@ -44,7 +44,7 @@ let
 
   maketar = targets:
     pkgsBuild.stdenv.mkDerivation {
-      name = "maketar";
+      name = "nix-portable-store-tarball";
       nativeBuildInputs = [ pkgsBuild.perl pkgsBuild.zstd ];
       exportReferencesGraph = map (x: [("closure-" + baseNameOf x) x]) targets;
       buildCommand = ''
@@ -95,6 +95,8 @@ let
 
     set -eo pipefail
 
+    start=\$(date +%s%N)  # start time in nanoseconds
+
     # dump environment on exit if debug is enabled
     if [ -n "\$NP_DEBUG" ] && [ "\$NP_DEBUG" -ge 1 ]; then
       trap "declare -p > /tmp/np_env" EXIT
@@ -344,11 +346,25 @@ let
     debug "proot executable: \$NP_PROOT"
     debug "testing all available runtimes..."
     if [ -z "\$NP_RUNTIME" ]; then
+      # read last automatic selected runtime from disk
+      if [ "\$newNPVersion" == "true" ]; then
+        debug "removing cached auto selected runtime"
+        rm -f "\$dir/conf/last_auto_runtime"
+      fi
+      if [ -f "\$dir/conf/last_auto_runtime" ]; then
+        last_auto_runtime="\$(cat "\$dir/conf/last_auto_runtime")"
+      else
+        last_auto_runtime=
+      fi
+      debug "last auto selected runtime: \$last_auto_runtime"
+      if [ "\$last_auto_runtime" != "" ]; then
+        NP_RUNTIME="\$last_auto_runtime"
       # check if nix --store works
-      mkdir -p \$dir/tmp/
-      touch \$dir/tmp/testfile
-      debug "testing nix --store"
-      if "\$NP_NIX" --store "\$dir/tmp/__store" shell -f "\$dir/mini-drv.nix" -c "\$dir/bin/nix" store add-file --store "\$dir/tmp/__store" "\$dir/tmp/testfile" >/dev/null 2>&3; then
+      elif \\
+          debug "testing nix --store" \\
+          && mkdir -p \$dir/tmp/ \\
+          && touch \$dir/tmp/testfile \\
+          && "\$NP_NIX" --store "\$dir/tmp/__store" shell -f "\$dir/mini-drv.nix" -c "\$dir/bin/nix" store add-file --store "\$dir/tmp/__store" "\$dir/tmp/testfile" >/dev/null 2>&3; then
         chmod -R +w \$dir/tmp/__store
         rm -r \$dir/tmp/__store
         debug "nix --store works on this system -> will use nix as runtime"
@@ -363,6 +379,7 @@ let
         debug "bwrap doesn't work on this system -> will use proot"
         NP_RUNTIME=proot
       fi
+      echo -n "\$NP_RUNTIME" > "\$dir/conf/last_auto_runtime"
     else
       debug "runtime selected via NP_RUNTIME: \$NP_RUNTIME"
     fi
@@ -540,6 +557,14 @@ let
     fi
 
 
+    ### print elapsed time
+    end=\$(date +%s%N)  # end time in nanoseconds
+    # time elapsed in millis with two decimal places
+    # elapsed=\$(echo "scale=2; (\$end - \$start)/1000000000" | bc)
+    elapsed=\$(echo "scale=2; (\$end - \$start)/1000000" | bc)
+    debug "Time to initialize nix-portable: \$elapsed millis"
+
+
 
     ### run commands
     [ -z "\$NP_RUN" ] && NP_RUN="\$run"

flake.nix

@@ -162,8 +162,19 @@
       ({
 
         bundlers = forAllSystems (system: pkgs: {
-          default = drv: self.packages.${system}.nix-portable.override {
+          # bundle with fast compression by default
+          default = self.bundlers.${system}.zstd-fast;
+          zstd-fast = drv: self.packages.${system}.nix-portable.override {
             bundledPackage = drv;
+            compression = "zstd -3 -T0";
+          };
+          zstd-max = drv: self.packages.${system}.nix-portable.override {
+            bundledPackage = drv;
+            compression = "zstd -19 -T0";
+          };
+          xz-max = drv: self.packages.${system}.nix-portable.override {
+            bundledPackage = drv;
+            compression = "xz -9 -T0";
           };
         });
 
@@ -180,7 +191,18 @@
         );
 
         packages = forAllSystems (system: pkgs: {
-          nix-portable = nixPortableForSystem { inherit system; };
+          nix-portable = (nixPortableForSystem { inherit system; }).override {
+            # all non x86_64-linux systems are built via emulation
+            #   -> decrease compression level to reduce CI build time
+            compression =
+              if system == "x86_64-linux"
+              then "zstd -19 -T0"
+              else "zstd -9 -T0";
+          };
+          # dev version that builds faster
+          nix-portable-dev = self.packages.${system}.nix-portable.override {
+            compression = "zstd -3 -T1";
+          };
         });
 
         defaultPackage = forAllSystems (system: pkgs: