linux-kernel - [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated physical CPUs are available

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Date:   Thu,  1 Aug 2019 15:06:36 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated physical CPUs are available

From: Wanpeng Li <wanpengli@...cent.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@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 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;
-- 
2.7.4