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);
+#endif
Maybe 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.
+
#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.
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.
