From 3eabfc175e804425989ca248257ed142a8bcf1df Mon Sep 17 00:00:00 2001
From: Michael Tuexen <tuexen@fh-muenster.de>
Date: Mon, 14 Nov 2016 04:13:05 +0100
Subject: [PATCH] Improve the precision when waiting for an event.
Sponsored by: Netflix
---
gtests/net/packetdrill/run.c | 20 +++++++++++++++++++-
1 file changed, 19 insertions(+), 1 deletion(-)
diff --git a/gtests/net/packetdrill/run.c b/gtests/net/packetdrill/run.c
index 0a7d3751..54f4ebbd 100644
--- a/gtests/net/packetdrill/run.c
+++ b/gtests/net/packetdrill/run.c
@@ -62,7 +62,11 @@
* sequence that wait_for_event() must execute while waiting
* for the next event.
*/
+#if defined(__FreeBSD__)
+const int MAX_SPIN_USECS = 100;
+#else
const int MAX_SPIN_USECS = 20;
+#endif
static struct state *state = NULL;
@@ -328,7 +332,7 @@ void wait_for_event(struct state *state)
* that we know has a fine-grained usleep(), then
* usleep() instead of spinning on the CPU.
*/
-#if defined(linux) || defined(__FreeBSD__)
+#if defined(linux)
/* Since the scheduler may not wake us up precisely
* when we tell it to, sleep until just before the
* event we're waiting for and then spin.
@@ -337,6 +341,20 @@ void wait_for_event(struct state *state)
usleep(wait_usecs - MAX_SPIN_USECS);
}
#endif
+#if defined(__FreeBSD__)
+ /* Since the scheduler may not wake us up precisely
+ * when we tell it to, sleep until just before the
+ * event we're waiting for and then spin.
+ * Since FreeBSD is overshooting by about 10 percent,
+ * take this into account.
+ */
+ if (wait_usecs > MAX_SPIN_USECS) {
+ useconds_t delta = (useconds_t)(wait_usecs - MAX_SPIN_USECS);
+
+ delta -= delta >> 3;
+ usleep(delta);
+ }
+#endif
/* At this point we should only have a millisecond or
* two to wait, so we spin.
--
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