[PATCH] smpboot: reuse timer calibration

[PATCH] smpboot: reuse timer calibration

[Paul Menzel]

From: Arjan van de Ven <arjan@linux.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@molgen.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

Re: [PATCH] smpboot: reuse timer calibration

[Peter Zijlstra]

On Tue, Oct 29, 2019 at 03:19:57PM +0100, Paul Menzel wrote:
> From: Arjan van de Ven <arjan@linux.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@molgen.mpg.de>
> ---
> 
> Arjan, can your Signed-off-by line be added? On what device, did you test
> this?

This patch makes no sense what so ever given the current function, also
it hard codes 0 as being the BSP.

All of this for platforms (!constant_tsc) that barely exist anymore.

Re: [PATCH] smpboot: reuse timer calibration

[Thomas Gleixner]

On Tue, 29 Oct 2019, Peter Zijlstra wrote:
> On Tue, Oct 29, 2019 at 03:19:57PM +0100, Paul Menzel wrote:
> > From: Arjan van de Ven <arjan@linux.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@molgen.mpg.de>
> > ---
> > 
> > Arjan, can your Signed-off-by line be added? On what device, did you test
> > this?
> 
> This patch makes no sense what so ever given the current function, also
> it hard codes 0 as being the BSP.
> 
> All of this for platforms (!constant_tsc) that barely exist anymore.

And it's only an issue on multi-socket systems with !constant_tsc, which
are even more rare.

Thanks,

	tglx