linux-kernel - [PATCH 1/2] kernel/sched: introduce vcpu preempted interface

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Message-Id: <1466937715-6683-2-git-send-email-xinhui.pan@linux.vnet.ibm.com>
Date:	Sun, 26 Jun 2016 06:41:54 -0400
From:	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	peterz@...radead.org, mingo@...hat.com, boqun.feng@...il.com,
	pan xinhui <xinhui.pan@...ux.vnet.ibm.com>
Subject: [PATCH 1/2] kernel/sched: introduce vcpu preempted interface

From: pan xinhui <xinhui.pan@...ux.vnet.ibm.com>

this supports to fix lock holder preempted issue which run as a guest

two interfaces,
bool vcpu_is_preempted(int cpu);
unsigned int vcpu_get_yield_count(int cpu);
arch may need implement anyone of them.

some spinneris may also need call need_yield_to(int cpu, unsigned int
old_yield_count) to know if it need stop the spinning.

Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
---
 include/linux/sched.h | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6e42ada..9c565d2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3293,6 +3293,40 @@ static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
 
 #endif /* CONFIG_SMP */
 
+#ifdef arch_vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+	return arch_vcpu_is_preempted(cpu);
+}
+#else
+static inline bool vcpu_is_preempted(int cpu)
+{
+	return 0;
+}
+#endif
+
+#ifdef arch_vcpu_get_yield_count
+static inline unsigned int vcpu_get_yield_count(int cpu)
+{
+	return arch_vcpu_get_yield_count(cpu);
+}
+#else
+static inline unsigned int vcpu_get_yield_count(int cpu)
+{
+	return 0;
+}
+#endif
+
+static inline bool
+need_yield_to(int vcpu, unsigned int old_yield_count)
+{
+	/* if we find the vcpu is preempted,
+	* then we may want to kick it, IOW, yield to it
+	*/
+	return vcpu_is_preempted(vcpu) ||
+		(vcpu_get_yield_count(vcpu) != old_yield_count);
+}
+
 extern long sched_setaffinity(pid_t pid, const struct cpumask *new_mask);
 extern long sched_getaffinity(pid_t pid, struct cpumask *mask);
 
-- 
2.4.11