linux-kernel - Re: [tip:x86/debug] x86/timers: Add simple udelay calibration

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Message-ID: <225381e1-5ad6-7208-697d-73cbb56163cc@siemens.com>
Date:   Wed, 24 May 2017 18:56:14 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     brgerst@...il.com, mathias.nyman@...ux.intel.com,
        dvlasenk@...hat.com, tglx@...utronix.de, peterz@...radead.org,
        bp@...en8.de, luto@...nel.org, torvalds@...ux-foundation.org,
        baolu.lu@...ux.intel.com, hpa@...or.com, jpoimboe@...hat.com,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        mingo@...nel.org, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/debug] x86/timers: Add simple udelay calibration

On 2017-03-21 13:19, tip-bot for Lu Baolu wrote:
> Commit-ID:  dd759d93f4dd4fd2f345a78ad1223bb3edf3ee7b
> Gitweb:     http://git.kernel.org/tip/dd759d93f4dd4fd2f345a78ad1223bb3edf3ee7b
> Author:     Lu Baolu <baolu.lu@...ux.intel.com>
> AuthorDate: Tue, 21 Mar 2017 16:01:29 +0800
> Committer:  Ingo Molnar <mingo@...nel.org>
> CommitDate: Tue, 21 Mar 2017 12:28:45 +0100
> 
> x86/timers: Add simple udelay calibration
> 
> Add a simple udelay calibration in x86 architecture-specific
> boot-time initializations. This will get a workable estimate
> for loops_per_jiffy. Hence, udelay() could be used after this
> initialization.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Acked-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Brian Gerst <brgerst@...il.com>
> Cc: Denys Vlasenko <dvlasenk@...hat.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Josh Poimboeuf <jpoimboe@...hat.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Mathias Nyman <mathias.nyman@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: linux-usb@...r.kernel.org
> Link: http://lkml.kernel.org/r/1490083293-3792-2-git-send-email-baolu.lu@linux.intel.com
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
>  arch/x86/kernel/setup.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 4bf0c89..e70204e 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -837,6 +837,26 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
>  	return 0;
>  }
>  
> +static void __init simple_udelay_calibration(void)
> +{
> +	unsigned int tsc_khz, cpu_khz;
> +	unsigned long lpj;
> +
> +	if (!boot_cpu_has(X86_FEATURE_TSC))
> +		return;
> +
> +	cpu_khz = x86_platform.calibrate_cpu();
> +	tsc_khz = x86_platform.calibrate_tsc();
> +
> +	tsc_khz = tsc_khz ? : cpu_khz;
> +	if (!tsc_khz)
> +		return;
> +
> +	lpj = tsc_khz * 1000;
> +	do_div(lpj, HZ);
> +	loops_per_jiffy = lpj;
> +}
> +
>  /*
>   * Determine if we were loaded by an EFI loader.  If so, then we have also been
>   * passed the efi memmap, systab, etc., so we should use these data structures
> @@ -985,6 +1005,8 @@ void __init setup_arch(char **cmdline_p)
>  	 */
>  	x86_configure_nx();
>  
> +	simple_udelay_calibration();
> +
>  	parse_early_param();
>  
>  #ifdef CONFIG_MEMORY_HOTPLUG
> 

Can we move this past init_hypervisor_platform()? Otherwise, the
x86_platform hooks aren't fully initialized yet, and we may use the
wrong functions.

Jan

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