[PATCH RESEND] KVM: Boosting vCPUs that are delivering interrupts

[Wanpeng Li <kernellwp@gmail.com>]

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