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Subject[PATCH 2/5] x86/kernel: Skip TSC test and error messages if already unstable
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.

Signed-off-by: Mike Travis <mike.travis@hpe.com>
Reviewed-by: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Reviewed-by: Russ Anderson <russ.anderson@hpe.com>
Reviewed-by: Peter Zijlstra <peterz@infradead.org>
---
v2: Add check_tsc_unstable to !CONFIG_SMP case.
Patches merged against 4.14.0-rc4
---
arch/x86/kernel/tsc_sync.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- linux.orig/arch/x86/kernel/tsc_sync.c
+++ linux/arch/x86/kernel/tsc_sync.c
@@ -52,6 +52,10 @@ 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;
@@ -114,6 +118,10 @@ bool __init tsc_store_and_check_tsc_adju
if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST))
return false;

+ /* Skip unnecessary error messages if TSC already unstable */
+ if (check_tsc_unstable())
+ return false;
+
rdmsrl(MSR_IA32_TSC_ADJUST, bootval);
cur->bootval = bootval;
cur->nextcheck = jiffies + HZ;
--

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