Hi, Baibir
	sorry for late responce, I missed reading your mail.

在 16/7/6 18:54, Balbir Singh 写道:

On Tue, 2016-06-28 at 10:43 -0400, Pan Xinhui wrote:

quoted

This is to fix some lock holder preemption issues. Some other locks
implementation do a spin loop before acquiring the lock itself. Currently
kernel has an interface of bool vcpu_is_preempted(int cpu). It take the cpu

								^^ takes

quoted

as parameter and return true if the cpu is preempted. Then kernel can break
the spin loops upon on the retval of vcpu_is_preempted.

As kernel has used this interface, So lets support it.

Only pSeries need supoort it. And the fact is powerNV are built into same

		   ^^ support

quoted

kernel image with pSeries. So we need return false if we are runnig as
powerNV. The another fact is that lppaca->yiled_count keeps zero on

					  ^^ yield

quoted

powerNV. So we can just skip the machine type.

Blame on me, I indeed need avoid such typo..
thanks for pointing it out.

quoted

Suggested-by: Boqun Feng <redacted>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Pan Xinhui <redacted>
---
 arch/powerpc/include/asm/spinlock.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index 523673d..3ac9fcb 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h

@@ -52,6 +52,24 @@
 #define SYNC_IO
 #endif

+/*
+ * This support kernel to check if one cpu is preempted or not.
+ * Then we can fix some lock holder preemption issue.
+ */
+#ifdef CONFIG_PPC_PSERIES
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+	/*
+	 * pSeries and powerNV can be built into same kernel image. In
+	 * principle we need return false directly if we are running as
+	 * powerNV. However the yield_count is always zero on powerNV, So
+	 * skip such machine type check

Or you could use the ppc_md interface callbacks if required, but your
solution works as well

thanks, So I can keep my code as is.

thanks
xinhui

quoted

+	 */
+	return !!(be32_to_cpu(lppaca_of(cpu).yield_count) & 1);
+}
+#endif
+
 static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
 {
 	return lock.slock == 0;

Balbir Singh.