From: Stanislav Kinsburskii <skinsburskii@xxxxxxxxxxxxxxxxxxx>
>
> And have it preset.
> This change allows to significantly reduce time to bring up guest SMP
> configuration as well as make sure the guest won't get inaccurate
> calibration results due to "noisy neighbour" situation.
>
> Below are the numbers for 16 VCPU guest before the patch (~1300 msec)
>
> [ 0.562938] x86: Booting SMP configuration:
> ...
> [ 1.859447] smp: Brought up 1 node, 16 CPUs
>
> and after the patch (~130 msec):
>
> [ 0.445079] x86: Booting SMP configuration:
> ...
> [ 0.575035] smp: Brought up 1 node, 16 CPUs
>
> This change is inspired by commit 0293615f3fb9 ("x86: KVM guest: use
> paravirt function to calculate cpu khz").
This patch has been nagging at me a bit, and I finally did some further
checking. Looking at Linux guests on local Hyper-V and in Azure, I see
a dmesg output line like this during boot:
Calibrating delay loop (skipped), value calculated using timer frequency.. 5187.81 BogoMIPS (lpj=2593905)
We're already skipping the delay loop calculation because lpj_fine
is set in tsc_init(), using the results of get_loops_per_jiffy(). The
latter does exactly the same calculation as hv_preset_lpj() in
this patch.
Is this patch arising from an environment where tsc_init() is
skipped for some reason? Just trying to make sure we fully
when this patch is applicable, and when not.
Michael
>
> Signed-off-by: Stanislav Kinsburskiy <stanislav.kinsburskiy@xxxxxxxxx>
> CC: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
> CC: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu@xxxxxxxxxx>
> CC: Dexuan Cui <decui@xxxxxxxxxxxxx>
> CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> CC: Ingo Molnar <mingo@xxxxxxxxxx>
> CC: Borislav Petkov <bp@xxxxxxxxx>
> CC: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> CC: x86@xxxxxxxxxx
> CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
> CC: linux-hyperv@xxxxxxxxxxxxxxx
> CC: linux-kernel@xxxxxxxxxxxxxxx
> ---
> arch/x86/kernel/cpu/mshyperv.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index dedec2f23ad1..0282b2e96cc2 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -320,6 +320,21 @@ static void __init hv_smp_prepare_cpus(unsigned int
> max_cpus)
> }
> #endif
>
> +static void __init __maybe_unused hv_preset_lpj(void)
> +{
> + unsigned long khz;
> + u64 lpj;
> +
> + if (!x86_platform.calibrate_tsc)
> + return;
> +
> + khz = x86_platform.calibrate_tsc();
> +
> + lpj = ((u64)khz * 1000);
> + do_div(lpj, HZ);
> + preset_lpj = lpj;
> +}
> +
> static void __init ms_hyperv_init_platform(void)
> {
> int hv_max_functions_eax;
> @@ -521,6 +536,12 @@ static void __init ms_hyperv_init_platform(void)
>
> /* Register Hyper-V specific clocksource */
> hv_init_clocksource();
> +
> + /*
> + * Preset lpj to make calibrate_delay a no-op, which is turn helps to
> + * speed up secondary cores initialization.
> + */
> + hv_preset_lpj();
> #endif
> /*
> * TSC should be marked as unstable only after Hyper-V
>
