logd: clearAll by UID speedup

- If doing a clear, skip accounting
- Ensure for busy checking, behind a region lock for instance, only
  break out if there was something to do. Basically move the filter
  actions first, and defer checking the region lock to the ends of
  the loops.

Bug: 23711431
Change-Id: Icc984f406880633516fb17dda84188a30d092e01

logd/LogBuffer.cpp

@@ -377,6 +377,7 @@ public:
 bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
     LogTimeEntry *oldest = NULL;
     bool busy = false;
+    bool clearAll = pruneRows == ULONG_MAX;
 
     LogTimeEntry::lock();
 
@@ -394,29 +395,23 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
     LogBufferElementCollection::iterator it;
 
     if (caller_uid != AID_ROOT) {
+        // Only here if clearAll condition (pruneRows == ULONG_MAX)
         for(it = mLogElements.begin(); it != mLogElements.end();) {
             LogBufferElement *e = *it;
 
+            if ((e->getLogId() != id) || (e->getUid() != caller_uid)) {
+                ++it;
+                continue;
+            }
+
             if (oldest && (oldest->mStart <= e->getSequence())) {
                 oldest->triggerSkip_Locked(id, pruneRows);
                 busy = true;
                 break;
             }
 
-            if (e->getLogId() != id) {
-                ++it;
-                continue;
-            }
-
-            if (e->getUid() == caller_uid) {
-                it = erase(it);
-                pruneRows--;
-                if (pruneRows == 0) {
-                    break;
-                }
-            } else {
-                ++it;
-            }
+            it = erase(it);
+            pruneRows--;
         }
         LogTimeEntry::unlock();
         return busy;
@@ -424,7 +419,7 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
 
     // prune by worst offender by uid
     bool hasBlacklist = mPrune.naughty();
-    while (pruneRows > 0) {
+    while (!clearAll && (pruneRows > 0)) {
         // recalculate the worst offender on every batched pass
         uid_t worst = (uid_t) -1;
         size_t worst_sizes = 0;
@@ -589,7 +584,7 @@ bool LogBuffer::prune(log_id_t id, unsigned long pruneRows, uid_t caller_uid) {
     }
 
     bool whitelist = false;
-    bool hasWhitelist = mPrune.nice();
+    bool hasWhitelist = mPrune.nice() && !clearAll;
     it = mLogElements.begin();
     while((pruneRows > 0) && (it != mLogElements.end())) {
         LogBufferElement *e = *it;