zebra: reduce dplane_fpm_nl ctxqueue_mutex contention

Reduce code in the critical sections of fpm_nl_process() and
fpm_process_queue() to the bare minimum - basically only enqueue
and dequeue operations on the shared ctxqueue.

Signed-off-by: Duncan Eastoe <duncan.eastoe@att.com>

diff --git a/zebra/dplane_fpm_nl.c b/zebra/dplane_fpm_nl.c
index 261b859bf6da39a8f0bcc1bdcc1cbd475c8f1e46..bd7b604badebf396ce080c81ea2233bf77341881 100644 (file)
--- a/zebra/dplane_fpm_nl.c
+++ b/zebra/dplane_fpm_nl.c
@@ -1223,15 +1223,15 @@ static int fpm_process_queue(struct thread *t)
        struct fpm_nl_ctx *fnc = THREAD_ARG(t);
        struct zebra_dplane_ctx *ctx;
 
-       frr_mutex_lock_autounlock(&fnc->ctxqueue_mutex);
-
        while (true) {
                /* No space available yet. */
                if (STREAM_WRITEABLE(fnc->obuf) < NL_PKT_BUF_SIZE)
                        break;
 
                /* Dequeue next item or quit processing. */
-               ctx = dplane_ctx_dequeue(&fnc->ctxqueue);
+               frr_with_mutex (&fnc->ctxqueue_mutex) {
+                       ctx = dplane_ctx_dequeue(&fnc->ctxqueue);
+               }
                if (ctx == NULL)
                        break;
 
@@ -1435,12 +1435,17 @@ static int fpm_nl_process(struct zebra_dplane_provider *prov)
                 * anyway.
                 */
                if (fnc->socket != -1 && fnc->connecting == false) {
-                       frr_mutex_lock_autounlock(&fnc->ctxqueue_mutex);
-                       dplane_ctx_enqueue_tail(&fnc->ctxqueue, ctx);
-
-                       /* Account the number of contexts. */
+                       /*
+                        * Update the number of queued contexts *before*
+                        * enqueueing, to ensure counter consistency.
+                        */
                        atomic_fetch_add_explicit(&fnc->counters.ctxqueue_len,
                                                  1, memory_order_relaxed);
+
+                       frr_with_mutex (&fnc->ctxqueue_mutex) {
+                               dplane_ctx_enqueue_tail(&fnc->ctxqueue, ctx);
+                       }
+
                        cur_queue = atomic_load_explicit(
                                &fnc->counters.ctxqueue_len,
                                memory_order_relaxed);