* Rik van Riel <r...@redhat.com> wrote:
> --- a/arch/x86/kernel/cpu/hypervisor.c
> +++ b/arch/x86/kernel/cpu/hypervisor.c
> @@ -76,6 +76,8 @@ void __init init_hypervisor_platform(void)
>
> init_hypervisor(&boot_cpu_data);
>
> + init_guest_spinlock_delay();
> +
> if (x86_hyper->init_platform)
> x86_hyper->init_platform();
> }
> diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
> index 64e33ef..fbc5ff3 100644
> --- a/arch/x86/kernel/smp.c
> +++ b/arch/x86/kernel/smp.c
> @@ -116,8 +116,25 @@ static bool smp_no_nmi_ipi = false;
> #define DELAY_SHIFT 8
> #define DELAY_FIXED_1 (1<<DELAY_SHIFT)
> #define MIN_SPINLOCK_DELAY (1 * DELAY_FIXED_1)
> -#define MAX_SPINLOCK_DELAY (16000 * DELAY_FIXED_1)
> +#define MAX_SPINLOCK_DELAY_NATIVE (16000 * DELAY_FIXED_1)
> +#define MAX_SPINLOCK_DELAY_GUEST (16 * DELAY_FIXED_1)
> #define DELAY_HASH_SHIFT 6
> +
> +/*
> + * Modern Intel and AMD CPUs tell the hypervisor when a guest is
> + * spinning excessively on a spinlock. The hypervisor will then
> + * schedule something else, effectively taking care of the backoff
> + * for us. Doing our own backoff on top of the hypervisor's pause
> + * loop exit handling can lead to excessively long delays, and
> + * performance degradations. Limit the spinlock delay in virtual
> + * machines to a smaller value. Called from init_hypervisor_platform
> + */
> +static int __read_mostly max_spinlock_delay = MAX_SPINLOCK_DELAY_NATIVE;
> +void __init init_guest_spinlock_delay(void)
> +{
> + max_spinlock_delay = MAX_SPINLOCK_DELAY_GUEST;
> +}
The kernel build will be sad on !SMP configs.
Thanks,
Ingo
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