From 3a80fe2b3b31f537127b5393af89a549c4d815d9 Mon Sep 17 00:00:00 2001
From: Sepherosa Ziehau <sephe@dragonflybsd.org>
Date: Sat, 28 Oct 2017 14:46:31 +0800
Subject: [PATCH] x86_64: Add pauses in the TSC mpsync testing loop.

This fixes Intel N3450 deadlock in the tight rdtsc/IPI loop.

Suggested-by: dillon@
Tested-by: mneumann@
Dragonfly-bug: http://bugs.dragonflybsd.org/issues/3087
---
 sys/platform/pc64/isa/clock.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sys/platform/pc64/isa/clock.c b/sys/platform/pc64/isa/clock.c
index 3b9508ef1a..2368c4e58d 100644
--- a/sys/platform/pc64/isa/clock.c
+++ b/sys/platform/pc64/isa/clock.c
@@ -1277,10 +1277,12 @@ tsc_mpsync_test_loop(struct tsc_mpsync_arg *arg)
 		lwkt_cpusync_init(&cs, gd->gd_other_cpus,
 		    tsc_mpsync_test_remote, arg);
 		lwkt_cpusync_interlock(&cs);
+		cpu_pause();
 		arg->tsc_target = rdtsc_ordered();
 		cpu_mfence();
 		lwkt_cpusync_deinterlock(&cs);
 		crit_exit();
+		cpu_pause();
 
 		if (!arg->tsc_mpsync) {
 			kprintf("cpu%d: TSC is not MP synchronized @%u\n",
-- 
2.41.0