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Subject[PATCH RESEND] KVM: Boosting vCPUs that are delivering interrupts
Date
From: Wanpeng Li <wanpengli@tencent.com>

Inspired by commit 9cac38dd5d (KVM/s390: Set preempted flag during vcpu wakeup
and interrupt delivery), except the lock holder, we want to also boost vCPUs
that are delivering interrupts. Actually most smp_call_function_many calls are
synchronous ipi calls, the ipi target vCPUs are also good yield candidates.
This patch sets preempted flag during wakeup and interrupt delivery time.

Testing on 80 HT 2 socket Xeon Skylake server, with 80 vCPUs VM 80GB RAM:
ebizzy -M

vanilla boosting improved
1VM 23000 21232 -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 55%

w/ boosting + w/ pv sched yield(vanilla)

vanilla boosting improved
1844 5157 79%

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@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
virt/kvm/kvm_main.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b4ab59d..2c46705 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2404,8 +2404,10 @@ void kvm_vcpu_kick(struct kvm_vcpu *vcpu)
int me;
int cpu = vcpu->cpu;

- if (kvm_vcpu_wake_up(vcpu))
+ if (kvm_vcpu_wake_up(vcpu)) {
+ vcpu->preempted = true;
return;
+ }

me = get_cpu();
if (cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu))
--
2.7.4
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