Add cache performance testing

This should hopefully show how much of a difference, if any, caching
packages makes.  There's no automated comparison here, the test just
runs one install without a cache, then a second install with a cache,
then a human needs to look at what difference it makes.

.github/workflows/cache-perf.yml

@@ -0,0 +1,48 @@
+name: Cache performance testing
+
+# Only run manually: the purpose of this test is to check how much (if at all)
+# using the caches helps, and that's not something that needs doing often, and
+# it is something that's time consuming.
+on: workflow_dispatch
+
+# Avoid running at the same time as other actions that interfere with caches,
+# to avoid pollution.
+concurrency: caches
+
+jobs:
+  clear-caches:
+    uses: ./.github/workflows/clear-caches.yml
+    permissions:
+      actions: write
+
+  # There should now be no cache, so we can test how long it takes to do an
+  # install without a cache while building the cache for the later action.
+  install-without-cache:
+    runs-on: windows-latest
+    needs: clear-caches
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install a large set of Cygwin packages
+        uses: ./
+        with:
+          packages: >
+            biber doxygen evolution kde-dev-utils
+            mkvtoolnix-debuginfo nghttp x11vnc
+          package-cache: saveonly
+
+  install-with-cache:
+    runs-on: windows-latest
+    needs: install-without-cache
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install a large set of Cygwin packages
+        uses: ./
+        with:
+          packages: >
+            biber doxygen evolution kde-dev-utils
+            mkvtoolnix-debuginfo nghttp x11vnc
+          package-cache: enabled

.github/workflows/cache-test.yml

@@ -8,29 +8,9 @@ concurrency: caches
 
 jobs:
   clear-caches:
-    runs-on: ubuntu-latest
+    uses: ./.github/workflows/clear-caches.yml
     permissions:
       actions: write
-    steps:
-      # This will only delete up to 100 caches.  That should be far more than
-      # is ever needed.
-      - name: Delete cache entries
-        uses: actions/github-script@v6
-        with:
-          script: |
-            const response = await github.rest.actions.getActionsCacheList({
-              owner: context.repo.owner,
-              repo: context.repo.repo,
-              per_page: 100,
-              key: 'cygwin-install-action-packages-'
-            });
-            for (const cache of response.data.actions_caches) {
-              await github.rest.actions.deleteActionsCacheById({
-                owner: context.repo.owner,
-                repo: context.repo.repo,
-                cache_id: cache.id
-              });
-            }
 
   test-caching:
     runs-on: windows-latest
@@ -53,6 +33,8 @@ jobs:
     # saveonly    | yes (3) | no (7)
     # restoreonly | no (4)  | yes (8)
     steps:
+      - name: Checkout
+        uses: actions/checkout@v3
 
       - name: Install Cygwin + bash_completion, no caching
         uses: ./

.github/workflows/clear-caches.yml

@@ -0,0 +1,29 @@
+name: Clear Cygwin package caches
+
+on: workflow_call
+
+jobs:
+  clear-caches:
+    runs-on: ubuntu-latest
+    permissions:
+      actions: write
+    steps:
+      # This will only delete up to 100 caches.  That should be far more than
+      # is ever needed.
+      - name: Delete cache entries
+        uses: actions/github-script@v6
+        with:
+          script: |
+            const response = await github.rest.actions.getActionsCacheList({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              per_page: 100,
+              key: 'cygwin-install-action-packages-'
+            });
+            for (const cache of response.data.actions_caches) {
+              await github.rest.actions.deleteActionsCacheById({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                cache_id: cache.id
+              });
+            }