Prevent lwlock dtrace probes from unnecessary work

If dtrace is compiled in but disabled, the lwlock dtrace probes still
evaluate their arguments.  Since PostgreSQL 13, T_NAME(lock) does
nontrivial work, so it should be avoided if not needed.  To fix, make
these calls conditional on the *_ENABLED() macro corresponding to each
probe.

Reviewed-by: Craig Ringer 
Discussion: https://www.postgresql.org/message-id/CAGRY4nwxKUS_RvXFW-ugrZBYxPFFM5kjwKT5O+0+Stuga5b4+Q@mail.gmail.com

diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 2fa90cc0954d9e58f311c18d0e7e402ec900f16e..b391f8924dd72b38967973e212b9e4df60aab2a1 100644 (file)
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -1323,7 +1323,8 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
 #endif
 
        LWLockReportWaitStart(lock);
-       TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
+       if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
 
        for (;;)
        {
@@ -1345,7 +1346,8 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
        }
 #endif
 
-       TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
+       if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
        LWLockReportWaitEnd();
 
        LOG_LWDEBUG("LWLockAcquire", lock, "awakened");
@@ -1354,7 +1356,8 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
        result = false;
    }
 
-   TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), mode);
+   if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_ENABLED())
+       TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), mode);
 
    /* Add lock to list of locks held by this backend */
    held_lwlocks[num_held_lwlocks].lock = lock;
@@ -1405,14 +1408,16 @@ LWLockConditionalAcquire(LWLock *lock, LWLockMode mode)
        RESUME_INTERRUPTS();
 
        LOG_LWDEBUG("LWLockConditionalAcquire", lock, "failed");
-       TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL(T_NAME(lock), mode);
+       if (TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL(T_NAME(lock), mode);
    }
    else
    {
        /* Add lock to list of locks held by this backend */
        held_lwlocks[num_held_lwlocks].lock = lock;
        held_lwlocks[num_held_lwlocks++].mode = mode;
-       TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE(T_NAME(lock), mode);
+       if (TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE(T_NAME(lock), mode);
    }
    return !mustwait;
 }
@@ -1484,7 +1489,8 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
 #endif
 
            LWLockReportWaitStart(lock);
-           TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
+           if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
+               TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
 
            for (;;)
            {
@@ -1502,7 +1508,8 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
                Assert(nwaiters < MAX_BACKENDS);
            }
 #endif
-           TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
+           if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
+               TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
            LWLockReportWaitEnd();
 
            LOG_LWDEBUG("LWLockAcquireOrWait", lock, "awakened");
@@ -1532,7 +1539,8 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
        /* Failed to get lock, so release interrupt holdoff */
        RESUME_INTERRUPTS();
        LOG_LWDEBUG("LWLockAcquireOrWait", lock, "failed");
-       TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL(T_NAME(lock), mode);
+       if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL(T_NAME(lock), mode);
    }
    else
    {
@@ -1540,7 +1548,8 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
        /* Add lock to list of locks held by this backend */
        held_lwlocks[num_held_lwlocks].lock = lock;
        held_lwlocks[num_held_lwlocks++].mode = mode;
-       TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT(T_NAME(lock), mode);
+       if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT(T_NAME(lock), mode);
    }
 
    return !mustwait;
@@ -1700,7 +1709,8 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
 #endif
 
        LWLockReportWaitStart(lock);
-       TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), LW_EXCLUSIVE);
+       if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), LW_EXCLUSIVE);
 
        for (;;)
        {
@@ -1719,7 +1729,8 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
        }
 #endif
 
-       TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), LW_EXCLUSIVE);
+       if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
+           TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), LW_EXCLUSIVE);
        LWLockReportWaitEnd();
 
        LOG_LWDEBUG("LWLockWaitForVar", lock, "awakened");
@@ -1727,7 +1738,8 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
        /* Now loop back and check the status of the lock again. */
    }
 
-   TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), LW_EXCLUSIVE);
+   if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_ENABLED())
+       TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), LW_EXCLUSIVE);
 
    /*
     * Fix the process wait semaphore's count for any absorbed wakeups.
@@ -1870,7 +1882,8 @@ LWLockRelease(LWLock *lock)
        LWLockWakeup(lock);
    }
 
-   TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock));
+   if (TRACE_POSTGRESQL_LWLOCK_RELEASE_ENABLED())
+       TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock));
 
    /*
     * Now okay to allow cancel/die interrupts.