[Xen-devel] [PATCH 8/8] libxl: event: Move poller pipe emptying to the end of afterpoll

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

If a timer event callback causes this poller to be woken (not very
unlikely) we would go round the poll loop twice rather than once.

Do the poller pipe emptying at the end; this is slightly more
efficient because it can't cause any callbacks, so it happens after
all the callbacks have been run.

(This pipe-emptying has to happen in afterpoll rather than the
apparently more logical beforepoll, because the application calling
beforepoll doesn't constitute a promise to actually do anything.)

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
 tools/libxl/libxl_event.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index 4314191c3b..f59fbc719e 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -1326,12 +1326,6 @@ static void afterpoll_internal(libxl__egc *egc, 
libxl__poller *poller,
         fd_occurs(egc, efd, revents);
     }
 
-    if (afterpoll_check_fd(poller,fds,nfds, poller->wakeup_pipe[0],POLLIN)) {
-        poller->pipe_nonempty = 0;
-        int e = libxl__self_pipe_eatall(poller->wakeup_pipe[0]);
-        if (e) LIBXL__EVENT_DISASTER(egc, "read wakeup", e, 0);
-    }
-
     for (;;) {
         libxl__ev_time *etime = LIBXL_TAILQ_FIRST(&CTX->etimes);
         if (!etime)
@@ -1346,6 +1340,12 @@ static void afterpoll_internal(libxl__egc *egc, 
libxl__poller *poller,
 
         time_occurs(egc, etime, ERROR_TIMEDOUT);
     }
+
+    if (afterpoll_check_fd(poller,fds,nfds, poller->wakeup_pipe[0],POLLIN)) {
+        poller->pipe_nonempty = 0;
+        int e = libxl__self_pipe_eatall(poller->wakeup_pipe[0]);
+        if (e) LIBXL__EVENT_DISASTER(egc, "read wakeup", e, 0);
+    }
 }
 
 void libxl_osevent_afterpoll(libxl_ctx *ctx, int nfds, const struct pollfd 
*fds,
-- 
2.11.0


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