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Subject: Re: [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated
 physical CPUs are available
To:     "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Wanpeng Li <kernellwp@gmail.com>,
        Marcelo Tosatti <mtosatti@redhat.com>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Linux PM <linux-pm@vger.kernel.org>
References: <1564643196-7797-1-git-send-email-wanpengli@tencent.com>
 <7b1e3025-f513-7068-32ac-4830d67b65ac@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Date:   Thu, 1 Aug 2019 18:54:49 +0200
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On 01/08/19 18:51, Rafael J. Wysocki wrote:
> On 8/1/2019 9:06 AM, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpengli@tencent.com>
>>
>> The downside of guest side polling is that polling is performed even
>> with other runnable tasks in the host. However, even if poll in kvm
>> can aware whether or not other runnable tasks in the same pCPU, it
>> can still incur extra overhead in over-subscribe scenario. Now we can
>> just enable guest polling when dedicated pCPUs are available.
>>
>> Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Cc: Marcelo Tosatti <mtosatti@redhat.com>
>> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> 
> Paolo, Marcelo, any comments?

Yes, it's a good idea.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

> 
>> ---
>>   drivers/cpuidle/cpuidle-haltpoll.c   | 3 ++-
>>   drivers/cpuidle/governors/haltpoll.c | 2 +-
>>   2 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/cpuidle/cpuidle-haltpoll.c
>> b/drivers/cpuidle/cpuidle-haltpoll.c
>> index 9ac093d..7aee38a 100644
>> --- a/drivers/cpuidle/cpuidle-haltpoll.c
>> +++ b/drivers/cpuidle/cpuidle-haltpoll.c
>> @@ -53,7 +53,8 @@ static int __init haltpoll_init(void)
>>         cpuidle_poll_state_init(drv);
>>   -    if (!kvm_para_available())
>> +    if (!kvm_para_available() ||
>> +        !kvm_para_has_hint(KVM_HINTS_REALTIME))
>>           return 0;
>>         ret = cpuidle_register(&haltpoll_driver, NULL);
>> diff --git a/drivers/cpuidle/governors/haltpoll.c
>> b/drivers/cpuidle/governors/haltpoll.c
>> index 797477b..685c7007 100644
>> --- a/drivers/cpuidle/governors/haltpoll.c
>> +++ b/drivers/cpuidle/governors/haltpoll.c
>> @@ -141,7 +141,7 @@ static struct cpuidle_governor haltpoll_governor = {
>>     static int __init init_haltpoll(void)
>>   {
>> -    if (kvm_para_available())
>> +    if (kvm_para_available() && kvm_para_has_hint(KVM_HINTS_REALTIME))
>>           return cpuidle_register_governor(&haltpoll_governor);
>>         return 0;
> 
>