[PATCH 2/3] x86/kernel: Skip TSC test and error messages if already unstable

From: mike.travis
Date: Thu Sep 21 2017 - 16:22:39 EST


If the TSC has already been determined to be unstable, then checking
TSC ADJUST values is a waste of time and generates unnecessary error
messages (840 for a 16 socket Skylake 28/2 core/ht system).

Signed-off-by: Mike Travis <mike.travis@xxxxxxx>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@xxxxxxx>
Reviewed-by: Russ Anderson <russ.anderson@xxxxxxx>
---
arch/x86/kernel/tsc_sync.c | 7 +++++++
1 file changed, 7 insertions(+)

--- linux.orig/arch/x86/kernel/tsc_sync.c
+++ linux/arch/x86/kernel/tsc_sync.c
@@ -38,6 +38,10 @@ void tsc_verify_tsc_adjust(bool resume)
if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
return;

+ /* Skip unnecessary error messages if TSC already unstable */
+ if (check_tsc_unstable())
+ return;
+
/* Rate limit the MSR check */
if (!resume && time_before(jiffies, adj->nextcheck))
return;
@@ -61,6 +65,9 @@ void tsc_verify_tsc_adjust(bool resume)
static void tsc_sanitize_first_cpu(struct tsc_adjust *cur, s64 bootval,
unsigned int cpu, bool bootcpu)
{
+ /* Skip unnecessary error messages if TSC already unstable */
+ if (check_tsc_unstable())
+ return;
/*
* First online CPU in a package stores the boot value in the
* adjustment value. This value might change later via the sync

--