0006-x86-don-t-check-for-random-warps-if-using-direct-syn.patch

From 65aa9d99b0ba0b2ce113ef67b39b37a2fae8c50d Mon Sep 17 00:00:00 2001
From: Steven Noonan <steven@uplinklabs.net>
Date: Wed, 17 Nov 2021 19:42:32 -0800
Subject: [PATCH 32/37] x86: don't check for random warps if using direct sync

There's some overhead in writing/reading MSR_IA32_TSC. We try to account
for it, but sometimes it under or over estimates the overhead, and we retry
syncing, and it sees the clock "go backwards".

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
---
 arch/x86/kernel/tsc_sync.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c
index d9c4e48d93f6..9d7ab87666fe 100644
--- a/arch/x86/kernel/tsc_sync.c
+++ b/arch/x86/kernel/tsc_sync.c
@@ -407,7 +407,7 @@ void check_tsc_sync_source(int cpu)
 		pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n",
 			smp_processor_id(), cpu);
 
-	} else if (atomic_dec_and_test(&test_runs) || random_warps) {
+	} else if (atomic_dec_and_test(&test_runs) || (random_warps && !tsc_allow_direct_sync)) {
 		/* Force it to 0 if random warps brought us here */
 		atomic_set(&test_runs, 0);
 
-- 
2.39.0