Check if CPU time tracking is expected to work

This check will allow statsd to decide whether it should add a puller
for total CPU time tracking. Reading total CPU time on devices that does
not support CPU time tracking is wasteful, passing all zero times around
and recording "no data" state.

Bug: 174245730
Test: atest libtimeinstate_test
Test: cmd stats pull-source 10095
Change-Id: Ib6155af4cbd6c639d356118934237d7dfd76b3a8

3 files changed, 23 insertions, 2 deletions

diff --git a/libs/cputimeinstate/cputimeinstate.cpp b/libs/cputimeinstate/cputimeinstate.cpp
index 462f0db97b..7e9bb7d468 100644
--- a/libs/cputimeinstate/cputimeinstate.cpp
+++ b/libs/cputimeinstate/cputimeinstate.cpp
@@ -155,10 +155,14 @@ static bool initGlobals() {
     return true;
 }
 
-static bool attachTracepointProgram(const std::string &eventType, const std::string &eventName) {
+static int retrieveProgramFd(const std::string &eventType, const std::string &eventName) {
     std::string path = StringPrintf(BPF_FS_PATH "prog_time_in_state_tracepoint_%s_%s",
                                     eventType.c_str(), eventName.c_str());
-    int prog_fd = retrieveProgram(path.c_str());
+    return retrieveProgram(path.c_str());
+}
+
+static bool attachTracepointProgram(const std::string &eventType, const std::string &eventName) {
+    int prog_fd = retrieveProgramFd(eventType, eventName);
     if (prog_fd < 0) return false;
     return bpf_attach_tracepoint(prog_fd, eventType.c_str(), eventName.c_str()) >= 0;
 }
@@ -174,6 +178,17 @@ static std::optional<uint32_t> getPolicyFreqIdx(uint32_t policy) {
     return {};
 }
 
+// Check if tracking is expected to work without activating it.
+bool isTrackingUidTimesSupported() {
+    auto freqs = getCpuFreqs();
+    if (!freqs || freqs->empty()) return false;
+    if (gTracking) return true;
+    if (retrieveProgramFd("sched", "sched_switch") < 0) return false;
+    if (retrieveProgramFd("power", "cpu_frequency") < 0) return false;
+    if (retrieveProgramFd("sched", "sched_process_free") < 0) return false;
+    return true;
+}
+
 // Start tracking and aggregating data to be reported by getUidCpuFreqTimes and getUidsCpuFreqTimes.
 // Returns true on success, false otherwise.
 // Tracking is active only once a live process has successfully called this function; if the calling
diff --git a/libs/cputimeinstate/cputimeinstate.h b/libs/cputimeinstate/cputimeinstate.h
index 46de66936a..41453745a0 100644
--- a/libs/cputimeinstate/cputimeinstate.h
+++ b/libs/cputimeinstate/cputimeinstate.h
@@ -22,6 +22,7 @@
 namespace android {
 namespace bpf {
 
+bool isTrackingUidTimesSupported();
 bool startTrackingUidTimes();
 std::optional<std::vector<std::vector<uint64_t>>> getTotalCpuFreqTimes();
 std::optional<std::vector<std::vector<uint64_t>>> getUidCpuFreqTimes(uint32_t uid);
diff --git a/libs/cputimeinstate/testtimeinstate.cpp b/libs/cputimeinstate/testtimeinstate.cpp
index d25b2e9d6f..2112b10ebc 100644
--- a/libs/cputimeinstate/testtimeinstate.cpp
+++ b/libs/cputimeinstate/testtimeinstate.cpp
@@ -40,6 +40,11 @@ static constexpr uint64_t NSEC_PER_YEAR = NSEC_PER_SEC * 60 * 60 * 24 * 365;
 
 using std::vector;
 
+TEST(TimeInStateTest, IsTrackingSupported) {
+    isTrackingUidTimesSupported();
+    SUCCEED();
+}
+
 TEST(TimeInStateTest, TotalTimeInState) {
     auto times = getTotalCpuFreqTimes();
     ASSERT_TRUE(times.has_value());