libtimeinstate: add functions to read only recently-updated stats
Add getUidsUpdatedCpuFreqTimes and getUidsUpdatedConcurrentTimes,
which skip reading stats for UIDs that haven't been updated since
before a time passed in by their caller, and pass a new lastUpdate
time back to the caller. This is implemented by querying a new map
that holds the most recent update time for each new UID.
This approach has a potential race when a UID is updated after we have
already read its stats, but before we finish iterating through the
rest of the BPF map. By not skipping UIDs updated up to 1s before
lastUpdate, we improve the chance that such an update will be picked
up the next time getUidsUpdated*Times is called. Though this doesn't
completely eliminate the risk of a race, the consequences of the race
aren't that severe - we could undercount some runtimes by ~seconds at
worst, and only until the affected UID runs again.
Extend existing tests to check that these new functions behave like
the existing getUids*Times functions when passed a last update time of
0, and add new testcases to exercise the case where a nonzero last
update time is used.
Test: libtimeinstate_test passes
Bug: 138317993
Change-Id: I06ddf8bd7ab7812d067f3a1f5b2fbedeae016bfc
Signed-off-by: Connor O'Brien <connoro@google.com>
diff --git a/libs/cputimeinstate/cputimeinstate.cpp b/libs/cputimeinstate/cputimeinstate.cpp
index 1465296..05a462e 100644
--- a/libs/cputimeinstate/cputimeinstate.cpp
+++ b/libs/cputimeinstate/cputimeinstate.cpp
@@ -58,6 +58,7 @@
static std::set<uint32_t> gAllFreqs;
static unique_fd gTisMapFd;
static unique_fd gConcurrentMapFd;
+static unique_fd gUidLastUpdateMapFd;
static std::optional<std::vector<uint32_t>> readNumbersFromFile(const std::string &path) {
std::string data;
@@ -144,6 +145,10 @@
unique_fd{bpf_obj_get(BPF_FS_PATH "map_time_in_state_uid_concurrent_times_map")};
if (gConcurrentMapFd < 0) return false;
+ gUidLastUpdateMapFd =
+ unique_fd{bpf_obj_get(BPF_FS_PATH "map_time_in_state_uid_last_update_map")};
+ if (gUidLastUpdateMapFd < 0) return false;
+
gInitialized = true;
return true;
}
@@ -263,6 +268,18 @@
return out;
}
+static std::optional<bool> uidUpdatedSince(uint32_t uid, uint64_t lastUpdate,
+ uint64_t *newLastUpdate) {
+ uint64_t uidLastUpdate;
+ if (findMapEntry(gUidLastUpdateMapFd, &uid, &uidLastUpdate)) return {};
+ // Updates that occurred during the previous read may have been missed. To mitigate
+ // this, don't ignore entries updated up to 1s before *lastUpdate
+ constexpr uint64_t NSEC_PER_SEC = 1000000000;
+ if (uidLastUpdate + NSEC_PER_SEC < lastUpdate) return false;
+ if (uidLastUpdate > *newLastUpdate) *newLastUpdate = uidLastUpdate;
+ return true;
+}
+
// Retrieve the times in ns that each uid spent running at each CPU freq.
// Return contains no value on error, otherwise it contains a map from uids to vectors of vectors
// using the format:
@@ -271,6 +288,14 @@
// where ti_j_k is the ns uid i spent running on the jth cluster at the cluster's kth lowest freq.
std::optional<std::unordered_map<uint32_t, std::vector<std::vector<uint64_t>>>>
getUidsCpuFreqTimes() {
+ return getUidsUpdatedCpuFreqTimes(nullptr);
+}
+
+// Retrieve the times in ns that each uid spent running at each CPU freq, excluding UIDs that have
+// not run since before lastUpdate.
+// Return format is the same as getUidsCpuFreqTimes()
+std::optional<std::unordered_map<uint32_t, std::vector<std::vector<uint64_t>>>>
+getUidsUpdatedCpuFreqTimes(uint64_t *lastUpdate) {
if (!gInitialized && !initGlobals()) return {};
time_key_t key, prevKey;
std::unordered_map<uint32_t, std::vector<std::vector<uint64_t>>> map;
@@ -282,8 +307,14 @@
std::vector<std::vector<uint64_t>> mapFormat;
for (const auto &freqList : gPolicyFreqs) mapFormat.emplace_back(freqList.size(), 0);
+ uint64_t newLastUpdate = lastUpdate ? *lastUpdate : 0;
std::vector<tis_val_t> vals(gNCpus);
do {
+ if (lastUpdate) {
+ auto uidUpdated = uidUpdatedSince(key.uid, *lastUpdate, &newLastUpdate);
+ if (!uidUpdated.has_value()) return {};
+ if (!*uidUpdated) continue;
+ }
if (findMapEntry(gTisMapFd, &key, vals.data())) return {};
if (map.find(key.uid) == map.end()) map.emplace(key.uid, mapFormat);
@@ -299,8 +330,9 @@
}
}
prevKey = key;
- } while (!getNextMapKey(gTisMapFd, &prevKey, &key));
+ } while (prevKey = key, !getNextMapKey(gTisMapFd, &prevKey, &key));
if (errno != ENOENT) return {};
+ if (lastUpdate && newLastUpdate > *lastUpdate) *lastUpdate = newLastUpdate;
return map;
}
@@ -365,6 +397,15 @@
// where ai is the ns spent running concurrently with tasks on i other cpus and pi_j is the ns spent
// running on the ith cluster, concurrently with tasks on j other cpus in the same cluster.
std::optional<std::unordered_map<uint32_t, concurrent_time_t>> getUidsConcurrentTimes() {
+ return getUidsUpdatedConcurrentTimes(nullptr);
+}
+
+// Retrieve the times in ns that each uid spent running concurrently with each possible number of
+// other tasks on each cluster (policy times) and overall (active times), excluding UIDs that have
+// not run since before lastUpdate.
+// Return format is the same as getUidsConcurrentTimes()
+std::optional<std::unordered_map<uint32_t, concurrent_time_t>> getUidsUpdatedConcurrentTimes(
+ uint64_t *lastUpdate) {
if (!gInitialized && !initGlobals()) return {};
time_key_t key, prevKey;
std::unordered_map<uint32_t, concurrent_time_t> ret;
@@ -379,7 +420,13 @@
std::vector<concurrent_val_t> vals(gNCpus);
std::vector<uint64_t>::iterator activeBegin, activeEnd, policyBegin, policyEnd;
+ uint64_t newLastUpdate = lastUpdate ? *lastUpdate : 0;
do {
+ if (lastUpdate) {
+ auto uidUpdated = uidUpdatedSince(key.uid, *lastUpdate, &newLastUpdate);
+ if (!uidUpdated.has_value()) return {};
+ if (!*uidUpdated) continue;
+ }
if (findMapEntry(gConcurrentMapFd, &key, vals.data())) return {};
if (ret.find(key.uid) == ret.end()) ret.emplace(key.uid, retFormat);
@@ -405,8 +452,7 @@
std::plus<uint64_t>());
}
}
- prevKey = key;
- } while (!getNextMapKey(gConcurrentMapFd, &prevKey, &key));
+ } while (prevKey = key, !getNextMapKey(gConcurrentMapFd, &prevKey, &key));
if (errno != ENOENT) return {};
for (const auto &[key, value] : ret) {
if (!verifyConcurrentTimes(value)) {
@@ -414,6 +460,7 @@
if (val.has_value()) ret[key] = val.value();
}
}
+ if (lastUpdate && newLastUpdate > *lastUpdate) *lastUpdate = newLastUpdate;
return ret;
}
@@ -446,6 +493,8 @@
return false;
if (deleteMapEntry(gConcurrentMapFd, &key) && errno != ENOENT) return false;
}
+
+ if (deleteMapEntry(gUidLastUpdateMapFd, &uid) && errno != ENOENT) return false;
return true;
}