[S390] spinlock: check virtual cpu running status

This patch introduces a new function that checks the running status
of a cpu in a hypervisor. This status is not virtualized, so the check
is only correct if running in an LPAR. On acquiring a spinlock, if the
cpu holding the lock is scheduled by the hypervisor, we do a busy wait
on the lock. If it is not scheduled, we yield over to that cpu.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 37 insertions, 16 deletions

diff --git a/arch/s390/lib/spinlock.c b/arch/s390/lib/spinlock.c
index cff327f109a..91754ffb920 100644
--- a/arch/s390/lib/spinlock.c
+++ b/arch/s390/lib/spinlock.c
@@ -43,16 +43,24 @@ void arch_spin_lock_wait(arch_spinlock_t *lp)
 {
         int count = spin_retry;
         unsigned int cpu = ~smp_processor_id();
+        unsigned int owner;
 
         while (1) {
-                if (count-- <= 0) {
-                        unsigned int owner = lp->owner_cpu;
-                        if (owner != 0)
-                                _raw_yield_cpu(~owner);
-                        count = spin_retry;
+                owner = lp->owner_cpu;
+                if (!owner || smp_vcpu_scheduled(~owner)) {
+                        for (count = spin_retry; count > 0; count--) {
+                                if (arch_spin_is_locked(lp))
+                                        continue;
+                                if (_raw_compare_and_swap(&lp->owner_cpu, 0,
+                                                          cpu) == 0)
+                                        return;
+                        }
+                        if (MACHINE_IS_LPAR)
+                                continue;
                 }
-                if (arch_spin_is_locked(lp))
-                        continue;
+                owner = lp->owner_cpu;
+                if (owner)
+                        _raw_yield_cpu(~owner);
                 if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
                         return;
         }
@@ -63,17 +71,27 @@ void arch_spin_lock_wait_flags(arch_spinlock_t *lp, unsigned long flags)
 {
         int count = spin_retry;
         unsigned int cpu = ~smp_processor_id();
+        unsigned int owner;
 
         local_irq_restore(flags);
         while (1) {
-                if (count-- <= 0) {
-                        unsigned int owner = lp->owner_cpu;
-                        if (owner != 0)
-                                _raw_yield_cpu(~owner);
-                        count = spin_retry;
+                owner = lp->owner_cpu;
+                if (!owner || smp_vcpu_scheduled(~owner)) {
+                        for (count = spin_retry; count > 0; count--) {
+                                if (arch_spin_is_locked(lp))
+                                        continue;
+                                local_irq_disable();
+                                if (_raw_compare_and_swap(&lp->owner_cpu, 0,
+                                                          cpu) == 0)
+                                        return;
+                                local_irq_restore(flags);
+                        }
+                        if (MACHINE_IS_LPAR)
+                                continue;
                 }
-                if (arch_spin_is_locked(lp))
-                        continue;
+                owner = lp->owner_cpu;
+                if (owner)
+                        _raw_yield_cpu(~owner);
                 local_irq_disable();
                 if (_raw_compare_and_swap(&lp->owner_cpu, 0, cpu) == 0)
                         return;
@@ -100,8 +118,11 @@ EXPORT_SYMBOL(arch_spin_trylock_retry);
 void arch_spin_relax(arch_spinlock_t *lock)
 {
         unsigned int cpu = lock->owner_cpu;
-        if (cpu != 0)
-                _raw_yield_cpu(~cpu);
+        if (cpu != 0) {
+                if (MACHINE_IS_VM || MACHINE_IS_KVM ||
+                    !smp_vcpu_scheduled(~cpu))
+                        _raw_yield_cpu(~cpu);
+        }
 }
 EXPORT_SYMBOL(arch_spin_relax);