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

[Christian Borntraeger]

On 12.07.19 09:10, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> 
> 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
This certainly made sense for s390 so I guess that this also makes sense
for others.
Nnote we (s390) do not use kvm_vcpu_kick, so this should not cause
any issue for s390.


> 
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
>  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))
>