linux-kernel - [PATCH] smpboot: reuse timer calibration

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Message-ID: <ebb16cf3-128d-2515-a98a-a58db0c1f963@molgen.mpg.de>
Date:   Tue, 29 Oct 2019 15:19:57 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Arjan van de Ven <arjan@...ux.intel.com>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] smpboot: reuse timer calibration

From: Arjan van de Ven <arjan@...ux.intel.com>
Date: Wed, 11 Feb 2015 17:28:14 -0600

NO point recalibrating for known-constant tsc ...
saves 200ms+ of boot time.

Signed-off-by: Paul Menzel <pmenzel@...gen.mpg.de>
---

Arjan, can your Signed-off-by line be added? On what device, did you 
test this?

This upstreams the patch from Clear Linux.

https://github.com/clearlinux-pkgs/linux/blob/master/0108-smpboot-reuse-timer-calibration.patch

  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 c59454c382fd..42b07ed467d2 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1525,6 +1525,9 @@ 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;
-- 
2.24.0.rc1