From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
Inspired by commit 9cac38dd5d (KVM/s390: Set preempted flag during
vcpu wakeup and interrupt delivery), we want to also boost not just
lock holders but also vCPUs that are delivering interrupts. Most
smp_call_function_many calls are synchronous, so the IPI target vCPUs
are also good yield candidates. This patch introduces vcpu->ready to
boost vCPUs during wakeup and interrupt delivery time; unlike s390 we do
not reuse vcpu->preempted so that voluntarily preempted vCPUs are taken
into account by kvm_vcpu_on_spin, but vmx_vcpu_pi_put is not affected
(VT-d PI handles voluntary preemption separately, in pi_pre_block).
Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM:
ebizzy -M
vanilla boosting improved
1VM 21443 23520 9%
2VM 2800 8000 180%
3VM 1800 3100 72%
Testing on my Haswell desktop 8 HT, with 8 vCPUs VM 8GB RAM, two VMs,
one running ebizzy -M, the other running 'stress --cpu 2':
w/ boosting + w/o pv sched yield(vanilla)
vanilla boosting improved
1570 4000 155%
w/ boosting + w/ pv sched yield(vanilla)
vanilla boosting improved
1844 5157 179%
w/o boosting, perf top in VM:
72.33% [kernel] [k] smp_call_function_many
4.22% [kernel] [k] call_function_i
3.71% [kernel] [k] async_page_fault
w/ boosting, perf top in VM:
38.43% [kernel] [k] smp_call_function_many
6.31% [kernel] [k] async_page_fault
6.13% libc-2.23.so [.] __memcpy_avx_unaligned
4.88% [kernel] [k] call_function_interrupt
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
v2->v3: put it in kvm_vcpu_wake_up, use WRITE_ONCE
arch/s390/kvm/interrupt.c | 2 +-
include/linux/kvm_host.h | 1 +
virt/kvm/kvm_main.c | 9 +++++++--
3 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 9dde4d7d8704..26f8bf4a22a7 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1240,7 +1240,7 @@ void kvm_s390_vcpu_wakeup(struct kvm_vcpu *vcpu)
* The vcpu gave up the cpu voluntarily, mark it as a good
* yield-candidate.
*/
- vcpu->preempted = true;
+ WRITE_ONCE(vcpu->ready, true);
swake_up_one(&vcpu->wq);
vcpu->stat.halt_wakeup++;
}
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index c5da875f19e3..5c5b5867024c 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -318,6 +318,7 @@ struct kvm_vcpu {
} spin_loop;
#endif
bool preempted;
+ bool ready;
struct kvm_vcpu_arch arch;
struct dentry *debugfs_dentry;
};
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b4ab59dd6846..65665e13ab9a 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2387,6 +2387,7 @@ bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu)
wqp = kvm_arch_vcpu_wq(vcpu);
if (swq_has_sleeper(wqp)) {
swake_up_one(wqp);
+ WRITE_ONCE(vcpu->ready, true);
++vcpu->stat.halt_wakeup;
return true;
}
@@ -2500,7 +2501,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
continue;
} else if (pass && i > last_boosted_vcpu)
break;
- if (!READ_ONCE(vcpu->preempted))
+ if (!READ_ONCE(vcpu->ready))
continue;
if (vcpu == me)
continue;
@@ -4205,6 +4206,8 @@ static void kvm_sched_in(struct preempt_notifier *pn, int cpu)
if (vcpu->preempted)
vcpu->preempted = false;
+ if (vcpu->ready)
+ WRITE_ONCE(vcpu->ready, false);
kvm_arch_sched_in(vcpu, cpu);
@@ -4216,8 +4219,10 @@ static void kvm_sched_out(struct preempt_notifier *pn,
{
struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn);
- if (current->state == TASK_RUNNING)
+ if (current->state == TASK_RUNNING) {
vcpu->preempted = true;
+ WRITE_ONCE(vcpu->ready, true);
+ }
kvm_arch_vcpu_put(vcpu);
}
--
1.8.3.1
