Show ccache stats at the end of the build

Zero the ccache stats at the beginning of the build and then display the
ccache stats at the end of the build to see how effective ccache was.

Pavel Raiskup added the opt-in knob.

Signed-off-by: Brian J. Murrell <brian@interlinx.bc.ca>

docs/Plugin-CCache.md

@@ -17,6 +17,7 @@ The ccache plugin is enabled by default and has the following values built-in:
     config_opts['plugin_conf']['ccache_opts']['dir'] = "%(cache_topdir)s/%(root)s/ccache/u%(chrootuid)s/"
     config_opts['plugin_conf']['ccache_opts']['hashdir'] = True
     config_opts['plugin_conf']['ccache_opts']['debug'] = False
+    config_opts['plugin_conf']['ccache_opts']['show_stats'] = False
 
 To turn on ccache compression, use the following in a config file:
 
@@ -36,3 +37,7 @@ This option is available since Mock 5.7.
 Setting `debug` to `True` creates per-object debug files that are helpful when debugging unexpected cache misses.
 See [ccache documentation](https://ccache.dev/manual/4.10.html#config_debug).
 This option is available since Mock 5.7.
+
+If `show_stats` is set to True, Mock calls `ccache --zero-stats` first (before
+doing the build), and then calls `ccache --show-stats`.
+This option is available since Mock v5.7+.

mock/docs/site-defaults.cfg

@@ -247,6 +247,7 @@
 # config_opts['plugin_conf']['ccache_opts']['compress'] = None
 # config_opts['plugin_conf']['ccache_opts']['dir'] = "{{cache_topdir}}/{{root}}/ccache/u{{chrootuid}}/"
 # config_opts['plugin_conf']['ccache_opts']['hashdir'] = True
+# config_opts['plugin_conf']['ccache_opts']['show_stats'] = False
 # config_opts['plugin_conf']['ccache_opts']['debug'] = False
 # config_opts['plugin_conf']['yum_cache_enable'] = True
 # config_opts['plugin_conf']['yum_cache_opts'] = {}

mock/py/mockbuild/config.py

@@ -132,6 +132,7 @@ def setup_default_config_opts():
             'dir': "{{cache_topdir}}/{{root}}/ccache/u{{chrootuid}}/",
             'hashdir': True,
             'debug': False,
+            'show_stats': False,
         },
         'yum_cache_enable': True,
         'yum_cache_opts': {

mock/py/mockbuild/plugins/ccache.py

@@ -35,6 +35,7 @@ def __init__(self, plugins, conf, buildroot):
         buildroot.preexisting_deps.append("ccache")
         plugins.add_hook("prebuild", self._ccacheBuildHook)
         plugins.add_hook("preinit", self._ccachePreInitHook)
+        plugins.add_hook("postbuild", self._ccachePostBuildHook)
         buildroot.mounts.add(
             BindMountPoint(srcpath=self.ccachePath, bindpath=buildroot.make_chroot_path("/var/tmp/ccache")))
 
@@ -47,6 +48,11 @@ def __init__(self, plugins, conf, buildroot):
     @traceLog()
     def _ccacheBuildHook(self):
         self.buildroot.doChroot(["ccache", "-M", str(self.ccache_opts['max_cache_size'])], shell=False)
+        if not self.ccache_opts.get("show_stats"):
+            return
+        # zero ccache stats
+        getLog().info("Zero ccache stats:")
+        self.buildroot.doChroot(["ccache", "--zero-stats"], printOutput=True, shell=False)
 
     # set up the ccache dir.
     # we also set a few variables used by ccache to find the shared cache.
@@ -69,3 +75,11 @@ def _ccachePreInitHook(self):
         file_util.mkdirIfAbsent(self.buildroot.make_chroot_path('/var/tmp/ccache'))
         file_util.mkdirIfAbsent(self.ccachePath)
         self.buildroot.uid_manager.changeOwner(self.ccachePath, recursive=True)
+
+    # get some cache stats
+    def _ccachePostBuildHook(self):
+        """ show the cache hit stats """
+        if not self.ccache_opts.get("show_stats"):
+            return
+        getLog().info("ccache stats:")
+        self.buildroot.doChroot(["ccache", "--show-stats"], printOutput=True, shell=False)

releng/release-notes-next/ccache-show-stats.feature

@@ -0,0 +1,3 @@
+There's a new [ccache](Plugin-CCache) plugin option
+`config_opts['plugin_conf']['ccache_opts']['show_stats']`; if set to `True`,
+Mock prints the ccache statistics (hits/misses) to logs.