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, 12 insertions, 17 deletions

diff --git a/xlators/debug/io-stats/src/io-stats.c b/xlators/debug/io-stats/src/io-stats.c
index c0cd0e2477b..4864c67a101 100644
--- a/xlators/debug/io-stats/src/io-stats.c
+++ b/xlators/debug/io-stats/src/io-stats.c
@@ -74,7 +74,7 @@ struct ios_stat {
         char           *filename;
         gf_atomic_t     counters[IOS_STATS_TYPE_MAX];
         struct ios_stat_lat thru_counters [IOS_STATS_THRU_MAX];
-        int             refcnt;
+        gf_atomic_t     refcnt;
 };
 
 struct ios_stat_list {
@@ -333,13 +333,10 @@ ios_fd_ctx_set (fd_t *fd, xlator_t *this, struct ios_fd *iosfd)
 static int
 ios_stat_ref (struct ios_stat *iosstat)
 {
-        LOCK (&iosstat->lock);
-        {
-                iosstat->refcnt++;
-        }
-        UNLOCK (&iosstat->lock);
+        uint64_t refcnt = 0;
+        refcnt = GF_ATOMIC_INC (iosstat->refcnt);
 
-        return iosstat->refcnt;
+        return refcnt;
 }
 
 
@@ -347,18 +344,16 @@ static int
 ios_stat_unref (struct ios_stat *iosstat)
 {
         int cleanup = 0;
-        LOCK (&iosstat->lock);
-        {
-                iosstat->refcnt--;
-                if (iosstat->refcnt == 0) {
-                        if (iosstat->filename) {
-                                GF_FREE (iosstat->filename);
-                                iosstat->filename = NULL;
-                        }
-                        cleanup = 1;
+        uint64_t refcnt = 0;
+
+        refcnt = GF_ATOMIC_DEC (iosstat->refcnt);
+        if (refcnt == 0) {
+                if (iosstat->filename) {
+                        GF_FREE (iosstat->filename);
+                        iosstat->filename = NULL;
                 }
+                cleanup = 1;
         }
-        UNLOCK (&iosstat->lock);
 
         if (cleanup) {
                 LOCK_DESTROY (&iosstat->lock);