Re: [PATCH v2 3/3] LoongArch: KVM: Set vcpu_is_preempted() macro rather than function

[Huacai Chen]

Hi, Bibo,

On Tue, Mar 17, 2026 at 5:29 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>
> vcpu_is_preempted() is performance sensitive called in function
> osq_lock(), here set it as macro. So that parameter is not parsed
> at most time, it can avoid cache line thrashing across numa node.
>
> Here is part of unixbench result on 3C5000 DualWay machine with 32
> Cores and 2 Numa node.
>           origin    with patch    CONFIG_PARAVIRT disabled
> execl     6871.9    7134.2        7190.8
> fstime    425.5     959.9         956.1
>
> From the test result, with macro method it is almost the same with
> CONFIG_PARAVIRT disabled, and there is some improvment compared with
> function method.
>
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
>  arch/loongarch/include/asm/qspinlock.h | 27 +++++++++++++++++++++-----
>  arch/loongarch/kernel/paravirt.c       | 15 ++------------
>  2 files changed, 24 insertions(+), 18 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/qspinlock.h b/arch/loongarch/include/asm/qspinlock.h
> index 66244801db67..b5d7a038faf1 100644
> --- a/arch/loongarch/include/asm/qspinlock.h
> +++ b/arch/loongarch/include/asm/qspinlock.h
> @@ -5,8 +5,10 @@
>  #include <linux/jump_label.h>
>
>  #ifdef CONFIG_PARAVIRT
> -
> +#include <asm/kvm_para.h>
>  DECLARE_STATIC_KEY_FALSE(virt_spin_lock_key);
> +DECLARE_STATIC_KEY_FALSE(virt_preempt_key);
> +DECLARE_PER_CPU(struct kvm_steal_time, steal_time);
>
>  #define virt_spin_lock virt_spin_lock
>
> @@ -34,10 +36,25 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
>         return true;
>  }
>
> -#define vcpu_is_preempted vcpu_is_preempted
> -
> -bool vcpu_is_preempted(int cpu);
> -
> +/*
> + * Macro is better than inline function here
> + * With inline function, parameter cpu is parsed even though it is not used.
> + * This may cause cache line thrashing across NUMA node.
> + * With macro method, parameter cpu is parsed only when it is used.
What is the test result with inline function? If it isn't
significantly worse than with macro, we usually prefer inline
functions.



Huacai

> + */
> +#define vcpu_is_preempted(cpu)                                                 \
> +({                                                                             \
> +       bool __val;                                                             \
> +                                                                               \
> +       if (!static_branch_unlikely(&virt_preempt_key))                         \
> +               __val = false;                                                  \
> +       else {                                                                  \
> +               struct kvm_steal_time *src;                                     \
> +               src = &per_cpu(steal_time, cpu);                                \
> +               __val = !!(READ_ONCE(src->preempted) & KVM_VCPU_PREEMPTED);     \
> +       }                                                                       \
> +       __val;                                                                  \
> +})
>  #endif /* CONFIG_PARAVIRT */
>
>  #include <asm-generic/qspinlock.h>
> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
> index b74fe6db49ab..2d1206e486e2 100644
> --- a/arch/loongarch/kernel/paravirt.c
> +++ b/arch/loongarch/kernel/paravirt.c
> @@ -10,8 +10,8 @@
>  #include <asm/paravirt.h>
>
>  static int has_steal_clock;
> -static DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
> -static DEFINE_STATIC_KEY_FALSE(virt_preempt_key);
> +DEFINE_PER_CPU(struct kvm_steal_time, steal_time) __aligned(64);
> +DEFINE_STATIC_KEY_FALSE(virt_preempt_key);
>  DEFINE_STATIC_KEY_FALSE(virt_spin_lock_key);
>
>  static bool steal_acc = true;
> @@ -261,17 +261,6 @@ static int pv_time_cpu_down_prepare(unsigned int cpu)
>         return 0;
>  }
>
> -bool vcpu_is_preempted(int cpu)
> -{
> -       struct kvm_steal_time *src;
> -
> -       if (!static_branch_unlikely(&virt_preempt_key))
> -               return false;
> -
> -       src = &per_cpu(steal_time, cpu);
> -       return !!(src->preempted & KVM_VCPU_PREEMPTED);
> -}
> -EXPORT_SYMBOL(vcpu_is_preempted);
>  #endif
>
>  static void pv_cpu_reboot(void *unused)
> --
> 2.39.3
>