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

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Message-ID: <CANRm+Cyix-AzUO2+osGz+1M6vh=pjafjNQcrUBKWB5NOD853kQ@mail.gmail.com>
Date:	Thu, 19 May 2016 19:48:45 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Christian Borntraeger <borntraeger@...ibm.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

2016-05-19 19:42 GMT+08:00 Christian Borntraeger <borntraeger@...ibm.com>:
> 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?

Nice catch!

How about something like below:

+       if (vcpu->halt_poll_ns ||
+               (remaining != 0 && remaining < halt_poll_ns_base)) {

Regards,
Wanpeng Li