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Subject: Re: [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated
 physical CPUs are available
To:     Wanpeng Li <kernellwp@gmail.com>,
        Paolo Bonzini <pbonzini@redhat.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>
From:   "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Organization: Intel Technology Poland Sp. z o. o., KRS 101882, ul. Slowackiego
 173, 80-298 Gdansk
Message-ID: <7b1e3025-f513-7068-32ac-4830d67b65ac@intel.com>
Date:   Thu, 1 Aug 2019 18:51:10 +0200
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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?


> ---
>   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;