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

[Huacai Chen]

Hi, Bibo,

On Wed, Mar 11, 2026 at 11:21 AM 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.
I remember that I had suggested you define vcpu_is_preempted() in the
header file but you refused.

Huacai

>
> 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..305afd37cdcb 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.
> + */
> +#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 = !!(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
>
>