From: Florin Coras <fcoras@cisco.com>
Date: Wed, 1 Mar 2023 08:45:31 +0000 (-0800)
Subject: vcl: accept vcl spurious wakeup in epoll wait eventfd
X-Git-Tag: v23.10-rc0~204
X-Git-Url: https://gerrit.fd.io/r/gitweb?a=commitdiff_plain;h=7a1e95a3178943c8a3d2fe7f812f4710b13f7f4d;p=vpp.git

vcl: accept vcl spurious wakeup in epoll wait eventfd

Accept one spurious wakeup from vcl in epoll_pwait_eventfd to avoid
returning zero events to app without timeout.

Type: improvement

Signed-off-by: Florin Coras <fcoras@cisco.com>
Change-Id: I447c7f8176413c562be28605376a92d15e22a1f9
---

diff --git a/src/vcl/ldp.c b/src/vcl/ldp.c
index 3d4c01c7833..9e01ac95bec 100644
--- a/src/vcl/ldp.c
+++ b/src/vcl/ldp.c
@@ -2567,7 +2567,7 @@ ldp_epoll_pwait_eventfd (int epfd, struct epoll_event *events,
 			 int maxevents, int timeout, const sigset_t * sigmask)
 {
   ldp_worker_ctx_t *ldpw;
-  int libc_epfd, rv = 0, num_ev;
+  int libc_epfd, rv = 0, num_ev, vcl_wups = 0;
   vls_handle_t ep_vlsh;
 
   ldp_init_check ();
@@ -2651,6 +2651,7 @@ ldp_epoll_pwait_eventfd (int epfd, struct epoll_event *events,
       goto done;
     }
 
+epoll_again:
   rv = libc_epoll_pwait (libc_epfd, events, maxevents, timeout, sigmask);
   if (rv <= 0)
     goto done;
@@ -2668,6 +2669,9 @@ ldp_epoll_pwait_eventfd (int epfd, struct epoll_event *events,
 	  num_ev = vls_epoll_wait (ep_vlsh, &events[rv], maxevents - rv, 0);
 	  if (PREDICT_TRUE (num_ev > 0))
 	    rv += num_ev;
+	  /* Woken up by vcl but no events generated. Accept it once */
+	  if (rv == 0 && vcl_wups++ < 1)
+	    goto epoll_again;
 	  break;
 	}
     }