ci: switch scheduled jobs to nix built kernel

.github/actions/restore-kernel-cache/action.yml

@@ -0,0 +1,26 @@
+name: 'Restore kernel cache'
+description: 'Restore a previously built kernel cache, failing if not available'
+inputs:
+  git-repo:
+    required: true
+    type: string
+  branch:
+    required: true
+    type: string
+
+runs:
+  using: "composite"
+  steps:
+    - name: Get hash from repo/branch
+      run: echo "SCHED_EXT_KERNEL_COMMIT=$(git ls-remote ${{ inputs.git-repo }} heads/${{ inputs.branch }} | awk '{print $1}')" >> $GITHUB_ENV
+      shell: bash
+
+    - name: Load cache
+      uses: actions/cache/restore@v4
+      with:
+        fail-on-cache-miss: true
+        key: kernel-build-${{ env.SCHED_EXT_KERNEL_COMMIT }}-7
+        path:  |
+          linux/arch/x86/boot/bzImage
+          linux/usr/include
+          linux/**/*.h

.github/workflows/bpf-next-test.yml

@@ -6,74 +6,12 @@ on:
       - cron: "0 */6 * * *"
 
 jobs:
-  build-kernel-nix:
+  build-kernel:
     uses: ./.github/workflows/build-kernel.yml
     with:
       git-repo: "https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git"
       branch: for-next
 
-  build-kernel:
-    runs-on: ubuntu-24.04
-    steps:
-      # prevent cache permission errors
-      - run: sudo chown root /usr/bin/tar && sudo chmod u+s /usr/bin/tar
-      # redundancy to exit fast
-      - run: echo 'debconf debconf/frontend select Noninteractive' | sudo debconf-set-selections
-      - run: sudo apt-get update
-      - run: sudo apt-get install -y git --no-install-recommends
-      # get latest head commit of sched_ext for-next
-      - run: echo "SCHED_EXT_KERNEL_COMMIT=$(git ls-remote https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git heads/for-next | awk '{print $1}')" >> $GITHUB_ENV
-
-      - uses: actions/checkout@v4
-
-      # use cached kernel if available, create after job if not
-      - name: Cache Kernel
-        id: cache-kernel
-        uses: actions/cache@v4
-        with:
-          path: |
-            linux/arch/x86/boot/bzImage
-            linux/usr/include
-            linux/**/*.h
-          key: kernel-build-${{ env.SCHED_EXT_KERNEL_COMMIT }}-bpf-1
-
-      - if: ${{ steps.cache-kernel.outputs.cache-hit != 'true' }}
-        uses: ./.github/actions/install-deps-action
-
-      # cache virtiofsd (goes away w/ 24.04)
-      - name: Cache virtiofsd
-        id: cache-virtiofsd
-        uses: actions/cache@v4
-        with:
-          path: |
-            /usr/lib/virtiofsd
-          key: virtiofsd-binary
-      - if: ${{ steps.cache-virtiofsd.outputs.cache-hit != 'true' && steps.cache-kernel.outputs.cache-hit != 'true' }}
-        run: cargo install virtiofsd && sudo cp -a ~/.cargo/bin/virtiofsd /usr/lib/
-
-
-      - if: ${{ steps.cache-kernel.outputs.cache-hit != 'true' }}
-        name: Clone Kernel
-        # Get the latest sched-ext enabled kernel directly from the korg
-        # for-next branch
-        run: git clone --single-branch -b for-next --depth 1 https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git linux
-
-      # guard rail because we are caching
-      - if: ${{ steps.cache-kernel.outputs.cache-hit != 'true' }}
-        run: cd linux && git checkout ${{ env.SCHED_EXT_KERNEL_COMMIT }}
-
-      - if: ${{ steps.cache-kernel.outputs.cache-hit != 'true' }}
-      # Print the latest commit of the checked out sched-ext kernel
-        run: cd linux && git log -1 --pretty=format:"%h %ad %s" --date=short
-
-      - if: ${{ steps.cache-kernel.outputs.cache-hit != 'true' }}
-      # Build a minimal kernel (with sched-ext enabled) using virtme-ng
-        run: cd linux && vng -v --build --config ../.github/workflows/sched-ext.config
-
-      - if: ${{ steps.cache-kernel.outputs.cache-hit != 'true' }}
-      # Generate kernel headers
-        run: cd linux && make headers
-
   integration-test:
     runs-on: ubuntu-24.04
     needs: build-kernel
@@ -82,9 +20,15 @@ jobs:
             scheduler: [ scx_bpfland, scx_lavd, scx_layered, scx_rlfifo, scx_rustland, scx_rusty ]
           fail-fast: false
     steps:
+      - uses: actions/checkout@v4
+
+      - uses: ./.github/actions/restore-kernel-cache
+        with:
+          git-repo: "https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git"
+          branch: for-next
+
       # prevent cache permission errors
       - run: sudo chown root /usr/bin/tar && sudo chmod u+s /usr/bin/tar
-      - uses: actions/checkout@v4
       - uses: Swatinem/rust-cache@v2
         with:
           key: ${{ matrix.scheduler }}
@@ -101,25 +45,6 @@ jobs:
       - if: ${{ steps.cache-virtiofsd.outputs.cache-hit != 'true' }}
         run: cargo install virtiofsd && sudo cp -a ~/.cargo/bin/virtiofsd /usr/lib/
 
-      # get latest head commit of sched_ext for-next
-      - run: echo "SCHED_EXT_KERNEL_COMMIT=$(git ls-remote https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git heads/for-next | awk '{print $1}')" >> $GITHUB_ENV
-
-      # use cached kernel if available, create after job if not
-      - name: Cache Kernel
-        id: cache-kernel
-        uses: actions/cache@v4
-        with:
-          path: |
-            linux/arch/x86/boot/bzImage
-            linux/usr/include
-            linux/**/*.h
-          key: kernel-build-${{ env.SCHED_EXT_KERNEL_COMMIT }}-bpf-1
-
-      # need to re-run job when kernel head changes between build and test running.
-      - if: ${{ steps.cache-kernel.outputs.cache-hit != 'true' }}
-        name: exit if cache stale
-        run: exit -1
-
       # veristat
       - run: wget https://github.com/libbpf/veristat/releases/download/v0.3.2/veristat-v0.3.2-amd64.tar.gz
       - run: tar -xvf veristat-v0.3.2-amd64.tar.gz && sudo cp veristat /usr/bin/