[RocksDB] Introduce Fast Mutex option

Summary:
This diff adds an option to specify whether PTHREAD_MUTEX_ADAPTIVE_NP will be enabled for the rocksdb single big kernel lock. db_bench also have this option now.
Quickly tested 8 thread cpu bound 100 byte random read.
No fast mutex: ~750k/s ops
With fast mutex: ~880k/s ops

Test Plan: make check; db_bench; db_stress

Reviewers: dhruba

CC: MarkCallaghan, leveldb

Differential Revision: https://reviews.facebook.net/D11031

db/db_bench.cc

@@ -301,6 +301,10 @@ static bool FLAGS_advise_random_on_open =
 static auto FLAGS_compaction_fadvice =
   leveldb::Options().access_hint_on_compaction_start;
 
+// Use adaptive mutex
+static auto FLAGS_use_adaptive_mutex =
+  leveldb::Options().use_adaptive_mutex;
+
 namespace leveldb {
 
 // Helper for quickly generating random data.
@@ -1149,6 +1153,9 @@ unique_ptr<char []> GenerateKeyFromInt(int v, const char* suffix = "")
     options.allow_readahead_compactions = FLAGS_use_readahead_compactions;
     options.advise_random_on_open = FLAGS_advise_random_on_open;
     options.access_hint_on_compaction_start = FLAGS_compaction_fadvice;
+
+    options.use_adaptive_mutex = FLAGS_use_adaptive_mutex;
+
     Status s;
     if(FLAGS_read_only) {
       s = DB::OpenForReadOnly(options, FLAGS_db, &db_);
@@ -1958,6 +1965,9 @@ int main(int argc, char** argv) {
       else {
         fprintf(stdout, "Unknown compaction fadvice:%s\n", buf);
       }
+    } else if (sscanf(argv[i], "--use_adaptive_mutex=%d%c", &n, &junk) == 1
+               && (n == 0 || n ==1 )) {
+      FLAGS_use_adaptive_mutex = n;
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);

db/db_impl.cc

@@ -153,6 +153,7 @@ DBImpl::DBImpl(const Options& options, const std::string& dbname)
       internal_filter_policy_(options.filter_policy),
       owns_info_log_(options_.info_log != options.info_log),
       db_lock_(nullptr),
+      mutex_(options.use_adaptive_mutex),
       shutting_down_(nullptr),
       bg_cv_(&mutex_),
       mem_(new MemTable(internal_comparator_, NumberLevels())),

include/leveldb/options.h

@@ -451,6 +451,14 @@ struct Options {
   // It will be applied to all input files of a compaction.
   // Default: NORMAL
   enum { NONE, NORMAL, SEQUENTIAL, WILLNEED } access_hint_on_compaction_start;
+
+  // Use adaptive mutex, which spins in the user space before resorting
+  // to kernel. This could reduce context switch when the mutex is not
+  // heavily contended. However, if the mutex is hot, we could end up
+  // wasting spin time.
+  // Default: false
+  bool use_adaptive_mutex;
+
 };
 
 // Options that control read operations

port/port_posix.cc

@@ -19,7 +19,24 @@ static void PthreadCall(const char* label, int result) {
   }
 }
 
-Mutex::Mutex() { PthreadCall("init mutex", pthread_mutex_init(&mu_, NULL)); }
+Mutex::Mutex(bool adaptive) {
+#ifdef OS_LINUX
+  if (!adaptive) {
+    PthreadCall("init mutex", pthread_mutex_init(&mu_, NULL));
+  } else {
+    pthread_mutexattr_t mutex_attr;
+    PthreadCall("init mutex attr", pthread_mutexattr_init(&mutex_attr));
+    PthreadCall("set mutex attr",
+                pthread_mutexattr_settype(&mutex_attr,
+                                          PTHREAD_MUTEX_ADAPTIVE_NP));
+    PthreadCall("init mutex", pthread_mutex_init(&mu_, &mutex_attr));
+    PthreadCall("destroy mutex attr",
+                pthread_mutexattr_destroy(&mutex_attr));
+  }
+#else // ignore adaptive for non-linux platform
+  PthreadCall("init mutex", pthread_mutex_init(&mu_, NULL));
+#endif // OS_LINUX
+}
 
 Mutex::~Mutex() { PthreadCall("destroy mutex", pthread_mutex_destroy(&mu_)); }
 

port/port_posix.h

@@ -82,7 +82,7 @@ class CondVar;
 
 class Mutex {
  public:
-  Mutex();
+  Mutex(bool adaptive = false);
   ~Mutex();
 
   void Lock();

util/options.cc

@@ -73,7 +73,8 @@ Options::Options()
       stats_dump_period_sec(3600),
       block_size_deviation (10),
       advise_random_on_open(true),
-      access_hint_on_compaction_start(NORMAL) {
+      access_hint_on_compaction_start(NORMAL),
+      use_adaptive_mutex(false) {
 }
 
 static const char* const access_hints[] = {
@@ -208,6 +209,8 @@ Options::Dump(Logger* log) const
         advise_random_on_open);
     Log(log,"         Options.access_hint_on_compaction_start: %s",
         access_hints[access_hint_on_compaction_start]);
+    Log(log,"                      Options.use_adaptive_mutex: %d",
+        use_adaptive_mutex);
 }   // Options::Dump
 
 //