[PATCH v3 1/4] kernel/sched: introduce vcpu preempted check interface

Pan Xinhui xinhui.pan at linux.vnet.ibm.com
Thu Jul 21 21:45:11 AEST 2016

This patch supports to fix lock holder preemption issue.

For kernel users, we could use bool vcpu_is_preempted(int cpu) to detech if
one vcpu is preempted or not.

The default implementation is a macro defined by false. So compiler can
wrap it out if arch dose not support such vcpu pteempted check.

Suggested-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com>
 include/linux/sched.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6e42ada..cbe0574 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3293,6 +3293,18 @@ static inline void set_task_cpu(struct task_struct *p, unsigned int cpu)
 #endif /* CONFIG_SMP */
+ * In order to deal with a various lock holder preemption issues provide an
+ * interface to see if a vCPU is currently running or not.
+ *
+ * This allows us to terminate optimistic spin loops and block, analogous to
+ * the native optimistic spin heuristic of testing if the lock owner task is
+ * running or not.
+ */
+#ifndef vcpu_is_preempted
+#define vcpu_is_preempted(cpu)	false
 extern long sched_setaffinity(pid_t pid, const struct cpumask *new_mask);
 extern long sched_getaffinity(pid_t pid, struct cpumask *mask);

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