glusterfs: Use gcc builtin ATOMIC operator to increase/decreate refcount.

Problem: In glusterfs code base we call mutex_lock/unlock to take
         reference/dereference for a object.Sometime it could be
         reason for lock contention also.

Solution: There is no need to use mutex to increase/decrease ref
          counter, instead of using mutex use gcc builtin ATOMIC
          operation.

Test:   I have not observed yet how much performance gain after apply
        this patch specific to glusterfs but i have tested same
        with below small program(mutex and atomic both) and
        get good difference.

static int numOuterLoops;
static void *
threadFunc(void *arg)
{
    int j;

    for (j = 0; j < numOuterLoops; j++) {
            __atomic_add_fetch (&glob, 1,__ATOMIC_ACQ_REL);
    }
    return NULL;
}

int
main(int argc, char *argv[])
{
    int opt, s, j;
    int numThreads;
    pthread_t *thread;
    int verbose;
    int64_t n = 0;

    if (argc < 2 ) {
     printf(" Please provide 2 args Num of threads && Outer Loop\n");
     exit (-1);
    }
    numThreads = atoi(argv[1]);
    numOuterLoops = atoi (argv[2]);

    if (1) {
        printf("\tthreads: %d; outer loops: %d;\n",
                numThreads, numOuterLoops);
    }

    thread = calloc(numThreads, sizeof(pthread_t));
    if (thread == NULL) {
        printf ("calloc error so exit\n");
        exit (-1);
    }

    __atomic_store (&glob, &n, __ATOMIC_RELEASE);
    for (j = 0; j < numThreads; j++) {
        s = pthread_create(&thread[j], NULL, threadFunc, NULL);
        if (s != 0) {
            printf ("pthread_create failed so exit\n");
            exit (-1);
        }
    }

    for (j = 0; j < numThreads; j++) {
        s = pthread_join(thread[j], NULL);
        if (s != 0) {
            printf ("pthread_join failed so exit\n");
            exit (-1);
        }
    }
    printf("glob value is %ld\n",__atomic_load_n (&glob,__ATOMIC_RELAXED));

    exit(0);
}

   time ./thr_count 800 800000
   threads: 800; outer loops: 800000;
   glob value is 640000000

real	1m10.288s
user	0m57.269s
sys	3m31.565s

time ./thr_count_atomic 800 800000
     threads: 800; outer loops: 800000;
glob value is 640000000

real	0m20.313s
user	1m20.558s
sys	0m0.028

Change-Id: Ie5030a52ea264875e002e108dd4b207b15ab7cc7
Signed-off-by: Mohit Agrawal <moagrawa@redhat.com>

1 files changed, 4 insertions, 8 deletions

diff --git a/libglusterfs/src/event-epoll.c b/libglusterfs/src/event-epoll.c
index 7fc53ffeaf6..45f724ab055 100644
--- a/libglusterfs/src/event-epoll.c
+++ b/libglusterfs/src/event-epoll.c
@@ -32,7 +32,7 @@ struct event_slot_epoll {
 	int fd;
 	int events;
 	int gen;
-	int ref;
+	gf_atomic_t ref;
 	int do_close;
 	int in_handler;
         int handled_error;
@@ -197,12 +197,7 @@ event_slot_get (struct event_pool *event_pool, int idx)
 		return NULL;
 
 	slot = &table[offset];
-
-	LOCK (&slot->lock);
-	{
-		slot->ref++;
-	}
-	UNLOCK (&slot->lock);
+        GF_ATOMIC_INC (slot->ref);
 
 	return slot;
 }
@@ -216,9 +211,10 @@ event_slot_unref (struct event_pool *event_pool, struct event_slot_epoll *slot,
 	int fd = -1;
 	int do_close = 0;
 
+        ref = GF_ATOMIC_DEC (slot->ref);
+
 	LOCK (&slot->lock);
 	{
-		ref = --slot->ref;
 		fd = slot->fd;
 		do_close = slot->do_close;
 	}