On 03/21/2017 04:01 AM, Lu Baolu wrote:
> 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.
This breaks Xen PV guests since at this point, and until
x86_init.paging.pagetable_init() which is when pvclock_vcpu_time_info is
mapped, they cannot access pvclock.
Is it reasonable to do this before tsc_init() is called? (The failure
has nothing to do with tsc_init(), really --- it's just that it is
called late enough that Xen PV guests get properly initialized.) If it
is, would it be possible to move simple_udelay_calibration() after
x86_init.paging.pagetable_init()?
-boris
>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
> 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
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