[PATCH v2] locking/pvqspinlock: Wait early if vCPU is preempted

From	Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Newsgroups	linux.kernel
Subject	[PATCH v2] locking/pvqspinlock: Wait early if vCPU is preempted
Date	2017-01-10 04:10 +0100
Message-ID	<sXUYV-4ej-11@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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If prev node is not in runnig state or its vCPU is preempted, we can give
up our vCPU slices ASAP in pv_wait_node. After commit d9345c65eb79
("sched/core: Introduce the vcpu_is_preempted(cpu) interface") kernel
has knowledge of one vCPU is running or not.

Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
---
v2:
  rewrite the commit message as Ingo pointed out the mistake.
---
 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

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[PATCH v2] locking/pvqspinlock: Wait early if vCPU is preempted Pan Xinhui <xinhui.pan@linux.vnet.ibm.com> - 2017-01-10 04:10 +0100
  [tip:locking/core] locking/pvqspinlock: Don't wait if vCPU is  preempted tip-bot for Pan Xinhui <tipbot@zytor.com> - 2017-01-12 11:10 +0100

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