common/buffer: replace RWLock with spinlocks

This decreases buffer::raw size by about 100 bytes (since RWLock occupies
104 bytes and simple_spinlock_t just 4) and also significantly decreases
time wasted by locking and unlocking, possibly reducing context switches too.
Particularly visible when using small blocksizes.

Signed-off-by: Piotr Dałek <piotr.dalek@ts.fujitsu.com>

diff --git a/src/common/buffer.cc b/src/common/buffer.cc
index e2de936d8c43410e58234381c87de172244de46d..864c7eefb9eb1c77f1d3fb4d5d65ba5f94e88753 100644 (file)
--- a/src/common/buffer.cc
+++ b/src/common/buffer.cc
@@ -162,16 +162,16 @@ static simple_spinlock_t buffer_debug_lock = SIMPLE_SPINLOCK_INITIALIZER;
     unsigned len;
     atomic_t nref;
 
-    mutable RWLock crc_lock;
+    mutable simple_spinlock_t crc_spinlock;
     map<pair<size_t, size_t>, pair<uint32_t, uint32_t> > crc_map;
 
     raw(unsigned l)
       : data(NULL), len(l), nref(0),
-       crc_lock("buffer::raw::crc_lock", false)
+       crc_spinlock(SIMPLE_SPINLOCK_INITIALIZER)
     { }
     raw(char *c, unsigned l)
       : data(c), len(l), nref(0),
-       crc_lock("buffer::raw::crc_lock", false)
+       crc_spinlock(SIMPLE_SPINLOCK_INITIALIZER)
     { }
     virtual ~raw() {}
 
@@ -208,32 +208,29 @@ static simple_spinlock_t buffer_debug_lock = SIMPLE_SPINLOCK_INITIALIZER;
     }
     bool get_crc(const pair<size_t, size_t> &fromto,
          pair<uint32_t, uint32_t> *crc) const {
-      crc_lock.get_read();
+      simple_spin_lock(&crc_spinlock);
       map<pair<size_t, size_t>, pair<uint32_t, uint32_t> >::const_iterator i =
       crc_map.find(fromto);
       if (i == crc_map.end()) {
-          crc_lock.unlock();
+          simple_spin_unlock(&crc_spinlock);
           return false;
       }
       *crc = i->second;
-      crc_lock.unlock();
+      simple_spin_unlock(&crc_spinlock);
       return true;
     }
     void set_crc(const pair<size_t, size_t> &fromto,
          const pair<uint32_t, uint32_t> &crc) {
-      crc_lock.get_write();
+      simple_spin_lock(&crc_spinlock);
       crc_map[fromto] = crc;
-      crc_lock.unlock();
+      simple_spin_unlock(&crc_spinlock);
     }
     void invalidate_crc() {
-      // don't own the write lock when map is empty
-      crc_lock.get_read();
+      simple_spin_lock(&crc_spinlock);
       if (crc_map.size() != 0) {
-        crc_lock.unlock();
-        crc_lock.get_write();
         crc_map.clear();
       }
-      crc_lock.unlock();
+      simple_spin_unlock(&crc_spinlock);
     }
   };