linux-kernel - [PATCH] locking/pvqspinlock: Wait early if vcpu is preempted

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Message-Id: <1481049850-42610-1-git-send-email-xinhui.pan@linux.vnet.ibm.com>
Date:   Tue,  6 Dec 2016 13:44:10 -0500
From:   Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...hat.com, peterz@...radead.org, longman@...hat.com,
        Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Subject: [PATCH] locking/pvqspinlock: Wait early if vcpu is preempted

If prev node is not in runnig state or its cpu is preempted, we need
wait early in pv_wait_node. After commit "sched/core: Introduce the
vcpu_is_preempted(cpu) interface" kernel has knowledge of one vcpu is
running or not. So lets use it.

Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
---
 kernel/locking/qspinlock_paravirt.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index e3b5520..48648dc 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -263,7 +263,8 @@ pv_wait_early(struct pv_node *prev, int loop)
 	if ((loop & PV_PREV_CHECK_MASK) != 0)
 		return false;
 
-	return READ_ONCE(prev->state) != vcpu_running;
+	return READ_ONCE(prev->state) != vcpu_running ||
+				vcpu_is_preempted(prev->cpu);
 }
 
 /*
-- 
2.4.11