[Xen-devel] [PATCH RFC 04/12] x86/ticketlock: make large and small ticket versions of spin_lock the same

[Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>]

Make the bulk of __ticket_spin_lock look identical for large and small
number of cpus.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 arch/x86/include/asm/spinlock.h |   23 ++++++++---------------
 1 files changed, 8 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 082990a..7586d7a 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -72,19 +72,16 @@ static __always_inline void __ticket_unlock_release(struct 
arch_spinlock *lock)
 #if (NR_CPUS < 256)
 static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
 {
-       register union {
-               struct __raw_tickets tickets;
-               unsigned short slock;
-       } inc = { .slock = 1 << TICKET_SHIFT };
+       register struct __raw_tickets inc = { .tail = 1 };
 
        asm volatile (LOCK_PREFIX "xaddw %w0, %1\n"
-                     : "+Q" (inc), "+m" (lock->slock) : : "memory", "cc");
+                     : "+r" (inc), "+m" (lock->tickets) : : "memory", "cc");
 
        for (;;) {
-               if (inc.tickets.head == inc.tickets.tail)
+               if (inc.head == inc.tail)
                        return;
                cpu_relax();
-               inc.tickets.head = ACCESS_ONCE(lock->tickets.head);
+               inc.head = ACCESS_ONCE(lock->tickets.head);
        }
        barrier();              /* make sure nothing creeps before the lock is 
taken */
 }
@@ -110,21 +107,17 @@ static __always_inline int 
__ticket_spin_trylock(arch_spinlock_t *lock)
 #else
 static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
 {
-       unsigned inc = 1 << TICKET_SHIFT;
-       __ticket_t tmp;
+       register struct __raw_tickets inc = { .tickets.tail = 1 };
 
        asm volatile(LOCK_PREFIX "xaddl %0, %1\n\t"
-                    : "+r" (inc), "+m" (lock->slock)
+                    : "+r" (inc), "+m" (lock->tickets)
                     : : "memory", "cc");
 
-       tmp = inc;
-       inc >>= TICKET_SHIFT;
-
        for (;;) {
-               if ((__ticket_t)inc == tmp)
+               if (inc.head == inc.tail)
                        return;
                cpu_relax();
-               tmp = ACCESS_ONCE(lock->tickets.head);
+               inc.head = ACCESS_ONCE(lock->tickets.head);
        }
        barrier();              /* make sure nothing creeps before the lock is 
taken */
 }
-- 
1.7.1.1



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