linux-kernel - [PATCH v5 3/6] powerpc: lib/locks.c: Add cpu yield/wake helper function

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Date:	Thu,  2 Jun 2016 17:26:27 +0800
From:	Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	virtualization@...ts.linux-foundation.org
Cc:	benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
	peterz@...radead.org, mingo@...hat.com, paulmck@...ux.vnet.ibm.com,
	waiman.long@....com, Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
Subject: [PATCH v5 3/6] powerpc: lib/locks.c: Add cpu yield/wake helper function

pv-qspinlock core has pv_wait/pv_kick which will give a better
performace by yielding and kicking cpu at some cases.
lets support them by adding two corresponding helper functions.

Signed-off-by: Pan Xinhui <xinhui.pan@...ux.vnet.ibm.com>
---
 arch/powerpc/include/asm/spinlock.h |  4 ++++
 arch/powerpc/lib/locks.c            | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index 4359ee6..3b65372 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -56,9 +56,13 @@
 /* We only yield to the hypervisor if we are in shared processor mode */
 #define SHARED_PROCESSOR (lppaca_shared_proc(local_paca->lppaca_ptr))
 extern void __spin_yield(arch_spinlock_t *lock);
+extern void __spin_yield_cpu(int cpu);
+extern void __spin_wake_cpu(int cpu);
 extern void __rw_yield(arch_rwlock_t *lock);
 #else /* SPLPAR */
 #define __spin_yield(x)	barrier()
+#define __spin_yield_cpu(x) barrier()
+#define __spin_wake_cpu(x) barrier()
 #define __rw_yield(x)	barrier()
 #define SHARED_PROCESSOR	0
 #endif
diff --git a/arch/powerpc/lib/locks.c b/arch/powerpc/lib/locks.c
index a9ebd71..3a58834 100644
--- a/arch/powerpc/lib/locks.c
+++ b/arch/powerpc/lib/locks.c
@@ -23,6 +23,39 @@
 #include <asm/hvcall.h>
 #include <asm/smp.h>
 
+void __spin_yield_cpu(int cpu)
+{
+	unsigned int holder_cpu = cpu, yield_count;
+
+	if (cpu == -1) {
+		plpar_hcall_norets(H_CONFER, -1, 0);
+		return;
+	}
+	BUG_ON(holder_cpu >= nr_cpu_ids);
+	yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
+	if ((yield_count & 1) == 0) {
+		/* if target cpu is running, confer slices to lpar*/
+		plpar_hcall_norets(H_CONFER, -1, 0);
+		return;
+	}
+	plpar_hcall_norets(H_CONFER,
+		get_hard_smp_processor_id(holder_cpu), yield_count);
+}
+EXPORT_SYMBOL_GPL(__spin_yield_cpu);
+
+void __spin_wake_cpu(int cpu)
+{
+	unsigned int holder_cpu = cpu, yield_count;
+
+	BUG_ON(holder_cpu >= nr_cpu_ids);
+	yield_count = be32_to_cpu(lppaca_of(holder_cpu).yield_count);
+	if ((yield_count & 1) == 0)
+		return;		/* virtual cpu is currently running */
+	plpar_hcall_norets(H_PROD,
+		get_hard_smp_processor_id(holder_cpu));
+}
+EXPORT_SYMBOL_GPL(__spin_wake_cpu);
+
 #ifndef CONFIG_QUEUED_SPINLOCKS
 void __spin_yield(arch_spinlock_t *lock)
 {
-- 
2.4.11