[PATCH v6 11/11] x86/smpboot: reuse timer calibration

[Usama Arif]

From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>

No point recalibrating for known-constant tsc.
When tested on a 128 core, 2 socket server, this reduces
the parallel smpboot time from 100ms to 30ms.

Not-signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Signed-off-by: Usama Arif <usama.arif@xxxxxxxxxxxxx>
---
 arch/x86/kernel/tsc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index a78e73da4a74..bab8a98080cf 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1569,6 +1569,9 @@ unsigned long calibrate_delay_is_known(void)
 	if (!constant_tsc || !mask)
 		return 0;
 
+	if (cpu != 0)
+		return cpu_data(0).loops_per_jiffy;
+
 	sibling = cpumask_any_but(mask, cpu);
 	if (sibling < nr_cpu_ids)
 		return cpu_data(sibling).loops_per_jiffy;
-- 
2.25.1