linux-kernel - Re: [PATCH v3] KVM: halt-polling: poll if emulated lapic timer will fire soon

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Date:	Tue, 24 May 2016 15:10:00 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	David Matlack <dmatlack@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Wanpeng Li <wanpeng.li@...mail.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	Yang Zhang <yang.zhang.wz@...il.com>
Subject: Re: [PATCH v3] KVM: halt-polling: poll if emulated lapic timer will
 fire soon

2016-05-24 14:59 GMT+08:00 Christian Borntraeger <borntraeger@...ibm.com>:
> On 05/24/2016 04:25 AM, Wanpeng Li wrote:
>> 2016-05-24 10:19 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
>>> 2016-05-24 2:01 GMT+08:00 David Matlack <dmatlack@...gle.com>:
>>>> On Sun, May 22, 2016 at 5:42 PM, Wanpeng Li <kernellwp@...il.com> wrote:
>>>>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>>>
>>>> I'm ok with this patch, but I'd like to better understand the target
>>>> workloads. What type of workloads do you expect to benefit from this?
>>>
>>> dynticks guests I think is one of workloads which can get benefit,
>>> there are lots of upcoming fire timers captured by my feature. Even
>>> during TCP testing. And also the workload of Yang's.
>>
>> Do you think I should add an module parameter to enable/disable it
>> during module insmod or current patch is fine?
>
> What about getting rid of this hunk
>
> -               val = 10000;
> +               val = halt_poll_ns_base;
>
>
> and then rename "halt_poll_ns_base" into "halt_poll_ns_timer" that
> can be changed as module parameter?

Good point,

>
>
> I also experimented with an s390 implementation, which seems pretty straightforward.
> It is probably something like the following (whitespace damaged due to pcopy/paste)
> and needs more testing.
>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 38bbc98..a97739d 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -682,6 +682,7 @@ void kvm_arch_async_page_present(struct kvm_vcpu *vcpu,
>                                  struct kvm_async_pf *work);
>
>  extern int sie64a(struct kvm_s390_sie_block *, u64 *);
> +extern u64 kvm_s390_timer_remaining(struct kvm_vcpu *vcpu);
>  extern char sie_exit;
>
>  static inline void kvm_arch_hardware_disable(void) {}
> @@ -699,7 +700,7 @@ static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>  static inline u64 kvm_arch_timer_remaining(struct kvm_vcpu *vcpu)
>  {
> -       return -1ULL;
> +       return kvm_s390_timer_remaining(vcpu);
>  }
>
>  void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu);
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index 5a80af7..5b209a2 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -936,6 +936,17 @@ static u64 __calculate_sltime(struct kvm_vcpu *vcpu)
>         return sltime;
>  }
>
> +
> +u64 kvm_s390_timer_remaining(struct kvm_vcpu *vcpu)
> +{
> +       u64 result;
> +
> +       preempt_disable();
> +       result = __calculate_sltime(vcpu);
> +       preempt_enable();
> +       return result;
> +}
> +
>  int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
>  {
>         u64 sltime;
>



-- 
Regards,
Wanpeng Li