On 2025/11/19 上午10:58, Huacai Chen wrote:
paravirt.h is included by header file asm/qspinlock.h on powerpc, however it is not so on loongarch :)On Wed, Nov 19, 2025 at 10:01 AM Bibo Mao <[email protected]> wrote:On 2025/11/18 下午8:48, Huacai Chen wrote:Hi, Bibo, On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <[email protected]> wrote:Function vcpu_is_preempted() is used to check whether vCPU is preempted or not. Here add implementation with vcpu_is_preempted() when option CONFIG_PARAVIRT is enabled. Signed-off-by: Bibo Mao <[email protected]> --- arch/loongarch/include/asm/smp.h | 1 + arch/loongarch/include/asm/spinlock.h | 5 +++++ arch/loongarch/kernel/paravirt.c | 16 ++++++++++++++++ arch/loongarch/kernel/smp.c | 6 ++++++ 4 files changed, 28 insertions(+) diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h index 3a47f52959a8..5b37f7bf2060 100644 --- a/arch/loongarch/include/asm/smp.h +++ b/arch/loongarch/include/asm/smp.h @@ -18,6 +18,7 @@ struct smp_ops { void (*init_ipi)(void); void (*send_ipi_single)(int cpu, unsigned int action); void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action); + bool (*vcpu_is_preempted)(int cpu); }; extern struct smp_ops mp_ops; diff --git a/arch/loongarch/include/asm/spinlock.h b/arch/loongarch/include/asm/spinlock.h index 7cb3476999be..c001cef893aa 100644 --- a/arch/loongarch/include/asm/spinlock.h +++ b/arch/loongarch/include/asm/spinlock.h @@ -5,6 +5,11 @@ #ifndef _ASM_SPINLOCK_H #define _ASM_SPINLOCK_H +#ifdef CONFIG_PARAVIRT +#define vcpu_is_preempted vcpu_is_preempted +bool vcpu_is_preempted(int cpu); +#endifMaybe paravirt.h is a better place?It is actually a little strange to add macro CONFIG_PARAVIRT in file asm/spinlock.h vcpu_is_preempted is originally defined in header file include/linux/sched.h like this #ifndef vcpu_is_preempted static inline bool vcpu_is_preempted(int cpu) { return false; } #endif that requires that header file is included before sched.h, file asm/spinlock.h can meet this requirement, however header file paravirt.h maybe it is not included before sched.h in generic. Here vcpu_is_preempted definition is added before the following including. #include <asm/processor.h> #include <asm/qspinlock.h> #include <asm/qrwlock.h> Maybe it is better to be added after the above header files including sentences, but need further investigation.powerpc put it in paravirt.h, so I think it is possible.
# grep paravirt.h arch/powerpc/* -r arch/powerpc/include/asm/paravirt_api_clock.h:#include <asm/paravirt.h> arch/powerpc/include/asm/qspinlock.h:#include <asm/paravirt.h> arch/powerpc/include/asm/simple_spinlock.h:#include <asm/paravirt.h> $ grep paravirt.h arch/loongarch/* -r arch/loongarch/include/asm/paravirt_api_clock.h:#include <asm/paravirt.h>
+ #include <asm/processor.h> #include <asm/qspinlock.h> #include <asm/qrwlock.h> diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c index b1b51f920b23..b99404b6b13f 100644 --- a/arch/loongarch/kernel/paravirt.c +++ b/arch/loongarch/kernel/paravirt.c @@ -52,6 +52,13 @@ static u64 paravt_steal_clock(int cpu) #ifdef CONFIG_SMP static struct smp_ops native_ops; +static bool pv_vcpu_is_preempted(int cpu) +{ + struct kvm_steal_time *src = &per_cpu(steal_time, cpu); + + return !!(src->preempted & KVM_VCPU_PREEMPTED); +} + static void pv_send_ipi_single(int cpu, unsigned int action) { int min, old; @@ -308,6 +315,9 @@ int __init pv_time_init(void) pr_err("Failed to install cpu hotplug callbacks\n"); return r; } + + if (kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT)) + mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted; #endif static_call_update(pv_steal_clock, paravt_steal_clock); @@ -332,3 +342,9 @@ int __init pv_spinlock_init(void) return 0; } + +bool notrace vcpu_is_preempted(int cpu) +{ + return mp_ops.vcpu_is_preempted(cpu); +}We can simplify the whole patch like this, then we don't need to touch smp.c, and we can merge Patch-2/3. +bool notrace vcpu_is_preempted(int cpu) +{ + if (!kvm_para_has_feature(KVM_FEATURE_PREEMPT_HINT)) + return false; + else { + struct kvm_steal_time *src = &per_cpu(steal_time, cpu); + return !!(src->preempted & KVM_VCPU_PREEMPTED); + } +}1. there is assembly output about relative vcpu_is_preempted <loongson_vcpu_is_preempted>: move $r4,$r0 jirl $r0,$r1,0 <pv_vcpu_is_preempted>: pcalau12i $r13,8759(0x2237) slli.d $r4,$r4,0x3 addi.d $r13,$r13,-1000(0xc18) ldx.d $r13,$r13,$r4 pcalau12i $r12,5462(0x1556) addi.d $r12,$r12,384(0x180) add.d $r12,$r13,$r12 ld.bu $r4,$r12,16(0x10) andi $r4,$r4,0x1 jirl $r0,$r1,0 <vcpu_is_preempted>: pcalau12i $r12,8775(0x2247) ld.d $r12,$r12,-472(0xe28) jirl $r0,$r12,0 andi $r0,$r0,0x0 <vcpu_is_preempted_new>: pcalau12i $r12,8151(0x1fd7) ld.d $r12,$r12,-1008(0xc10) bstrpick.d $r12,$r12,0x1a,0x1a beqz $r12,188(0xbc) # 900000000024ec60 pcalau12i $r12,11802(0x2e1a) addi.d $r12,$r12,-1400(0xa88) ldptr.w $r14,$r12,36(0x24) beqz $r14,108(0x6c) # 900000000024ec20 addi.w $r13,$r0,1(0x1) bne $r14,$r13,164(0xa4) # 900000000024ec60 ldptr.w $r13,$r12,40(0x28) bnez $r13,24(0x18) # 900000000024ebdc lu12i.w $r14,262144(0x40000) ori $r14,$r14,0x4 cpucfg $r14,$r14 slli.w $r13,$r14,0x0 st.w $r14,$r12,40(0x28) bstrpick.d $r13,$r13,0x3,0x3 beqz $r13,128(0x80) # 900000000024ec60 pcalau12i $r13,8759(0x2237) slli.d $r4,$r4,0x3 addi.d $r13,$r13,-1000(0xc18) ldx.d $r13,$r13,$r4 pcalau12i $r12,5462(0x1556) addi.d $r12,$r12,384(0x180) add.d $r12,$r13,$r12 ld.bu $r4,$r12,16(0x10) andi $r4,$r4,0x1 jirl $r0,$r1,0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 lu12i.w $r13,262144(0x40000) cpucfg $r13,$r13 lu12i.w $r15,1237(0x4d5) ori $r15,$r15,0x64b slli.w $r13,$r13,0x0 bne $r13,$r15,-124(0x3ff84) # 900000000024ebb8 addi.w $r13,$r0,1(0x1) st.w $r13,$r12,36(0x24) b -128(0xfffff80) # 900000000024ebc0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 andi $r0,$r0,0x0 move $r4,$r0 jirl $r0,$r1,0 With vcpu_is_preempted(), there is one memory load and one jirl jump, with vcpu_is_preempted_new(), there is two memory load and two beq compare instructions.Is vcpu_is_preempted() performance critical (we need performance data here)? It seems the powerpc version is also complex.2. In some scenery such nr_cpus == 1, loongson_vcpu_is_preempted() is better than pv_vcpu_is_preempted() even if the preempt feature is enabled.In your original patch, "mp_ops.vcpu_is_preempted = pv_vcpu_is_preempted" if the preempt feature is enabled. Why is loongson_vcpu_is_preempted() called when nr_cpus=1? HuacaiRegards Bibo MaoHuacai+EXPORT_SYMBOL(vcpu_is_preempted); diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c index 46036d98da75..f04192fedf8d 100644 --- a/arch/loongarch/kernel/smp.c +++ b/arch/loongarch/kernel/smp.c @@ -307,10 +307,16 @@ static void loongson_init_ipi(void) panic("IPI IRQ request failed\n"); } +static bool loongson_vcpu_is_preempted(int cpu) +{ + return false; +} + struct smp_ops mp_ops = { .init_ipi = loongson_init_ipi, .send_ipi_single = loongson_send_ipi_single, .send_ipi_mask = loongson_send_ipi_mask, + .vcpu_is_preempted = loongson_vcpu_is_preempted, }; static void __init fdt_smp_setup(void) -- 2.39.3
