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

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Date:	Thu, 19 May 2016 13:42:32 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Wanpeng Li <wanpeng.li@...mail.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH] KVM: halt-polling: poll if emulated lapic timer will fire
 soon

On 05/19/2016 01:35 PM, Wanpeng Li wrote:
> 2016-05-19 19:23 GMT+08:00 Christian Borntraeger <borntraeger@...ibm.com>:
>> On 05/19/2016 11:26 AM, Wanpeng Li wrote:
>>
>> I think in general a good idea to poll if a timer will expire soon.
>>
>> Some patch comments:
>>
>> Same for all non-x86 archs:
>>> +static inline unsigned int kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) {}
>>
>> A function returning int, without a return statement?
>> That gives at least a compiler warning.
> 
> How about return 0 for all non-x86 archs?

We will provide an s390 implementation soon, but until then a proper
default would be good.

[....]
>>> +     if (vcpu->halt_poll_ns || (remaining < halt_poll_ns_base)) {

but then remaining is 0 and the 2nd condition will always be true, no?