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 08:59:17 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Wanpeng Li <kernellwp@...il.com>,
	David Matlack <dmatlack@...gle.com>
Cc:	"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

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?




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;