Re: [PATCH RFC V9 8/19] x86/pvticketlock: When paravirtualizing ticket locks, increment by 2

2013-06-03 Thread Konrad Rzeszutek Wilk 
On Sun, Jun 02, 2013 at 12:54:02AM +0530, Raghavendra K T wrote:
 x86/pvticketlock: When paravirtualizing ticket locks, increment by 2
 
 From: Jeremy Fitzhardinge jeremy.fitzhardi...@citrix.com
 
 Increment ticket head/tails by 2 rather than 1 to leave the LSB free
 to store a is in slowpath state bit.  This halves the number
 of possible CPUs for a given ticket size, but this shouldn't matter
 in practice - kernels built for 32k+ CPU systems are probably
 specially built for the hardware rather than a generic distro
 kernel.
 
 Signed-off-by: Jeremy Fitzhardinge jeremy.fitzhardi...@citrix.com
 Tested-by: Attilio Rao attilio@citrix.com
 Signed-off-by: Raghavendra K T raghavendra...@linux.vnet.ibm.com

Reviewed-by: Konrad Rzeszutek Wilk konrad.w...@oracle.com
 ---
  arch/x86/include/asm/spinlock.h   |   10 +-
  arch/x86/include/asm/spinlock_types.h |   10 +-
  2 files changed, 14 insertions(+), 6 deletions(-)
 
 diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
 index 7442410..04a5cd5 100644
 --- a/arch/x86/include/asm/spinlock.h
 +++ b/arch/x86/include/asm/spinlock.h
 @@ -78,7 +78,7 @@ static __always_inline void __ticket_unlock_kick(struct 
 arch_spinlock *lock,
   */
  static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
  {
 - register struct __raw_tickets inc = { .tail = 1 };
 + register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
  
   inc = xadd(lock-tickets, inc);
  
 @@ -104,7 +104,7 @@ static __always_inline int 
 arch_spin_trylock(arch_spinlock_t *lock)
   if (old.tickets.head != old.tickets.tail)
   return 0;
  
 - new.head_tail = old.head_tail + (1  TICKET_SHIFT);
 + new.head_tail = old.head_tail + (TICKET_LOCK_INC  TICKET_SHIFT);
  
   /* cmpxchg is a full barrier, so nothing can move before it */
   return cmpxchg(lock-head_tail, old.head_tail, new.head_tail) == 
 old.head_tail;
 @@ -112,9 +112,9 @@ static __always_inline int 
 arch_spin_trylock(arch_spinlock_t *lock)
  
  static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
  {
 - __ticket_t next = lock-tickets.head + 1;
 + __ticket_t next = lock-tickets.head + TICKET_LOCK_INC;
  
 - __add(lock-tickets.head, 1, UNLOCK_LOCK_PREFIX);
 + __add(lock-tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
   __ticket_unlock_kick(lock, next);
  }
  
 @@ -129,7 +129,7 @@ static inline int arch_spin_is_contended(arch_spinlock_t 
 *lock)
  {
   struct __raw_tickets tmp = ACCESS_ONCE(lock-tickets);
  
 - return (__ticket_t)(tmp.tail - tmp.head)  1;
 + return (__ticket_t)(tmp.tail - tmp.head)  TICKET_LOCK_INC;
  }
  #define arch_spin_is_contended   arch_spin_is_contended
  
 diff --git a/arch/x86/include/asm/spinlock_types.h 
 b/arch/x86/include/asm/spinlock_types.h
 index 83fd3c7..e96fcbd 100644
 --- a/arch/x86/include/asm/spinlock_types.h
 +++ b/arch/x86/include/asm/spinlock_types.h
 @@ -3,7 +3,13 @@
  
  #include linux/types.h
  
 -#if (CONFIG_NR_CPUS  256)
 +#ifdef CONFIG_PARAVIRT_SPINLOCKS
 +#define __TICKET_LOCK_INC2
 +#else
 +#define __TICKET_LOCK_INC1
 +#endif
 +
 +#if (CONFIG_NR_CPUS  (256 / __TICKET_LOCK_INC))
  typedef u8  __ticket_t;
  typedef u16 __ticketpair_t;
  #else
 @@ -11,6 +17,8 @@ typedef u16 __ticket_t;
  typedef u32 __ticketpair_t;
  #endif
  
 +#define TICKET_LOCK_INC  ((__ticket_t)__TICKET_LOCK_INC)
 +
  #define TICKET_SHIFT (sizeof(__ticket_t) * 8)
  
  typedef struct arch_spinlock {
 
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[PATCH RFC V9 8/19] x86/pvticketlock: When paravirtualizing ticket locks, increment by 2

2013-06-01 Thread Raghavendra K T 
x86/pvticketlock: When paravirtualizing ticket locks, increment by 2

From: Jeremy Fitzhardinge jeremy.fitzhardi...@citrix.com

Increment ticket head/tails by 2 rather than 1 to leave the LSB free
to store a is in slowpath state bit.  This halves the number
of possible CPUs for a given ticket size, but this shouldn't matter
in practice - kernels built for 32k+ CPU systems are probably
specially built for the hardware rather than a generic distro
kernel.

Signed-off-by: Jeremy Fitzhardinge jeremy.fitzhardi...@citrix.com
Tested-by: Attilio Rao attilio@citrix.com
Signed-off-by: Raghavendra K T raghavendra...@linux.vnet.ibm.com
---
 arch/x86/include/asm/spinlock.h   |   10 +-
 arch/x86/include/asm/spinlock_types.h |   10 +-
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 7442410..04a5cd5 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -78,7 +78,7 @@ static __always_inline void __ticket_unlock_kick(struct 
arch_spinlock *lock,
  */
 static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
 {
-   register struct __raw_tickets inc = { .tail = 1 };
+   register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
 
inc = xadd(lock-tickets, inc);
 
@@ -104,7 +104,7 @@ static __always_inline int 
arch_spin_trylock(arch_spinlock_t *lock)
if (old.tickets.head != old.tickets.tail)
return 0;
 
-   new.head_tail = old.head_tail + (1  TICKET_SHIFT);
+   new.head_tail = old.head_tail + (TICKET_LOCK_INC  TICKET_SHIFT);
 
/* cmpxchg is a full barrier, so nothing can move before it */
return cmpxchg(lock-head_tail, old.head_tail, new.head_tail) == 
old.head_tail;
@@ -112,9 +112,9 @@ static __always_inline int 
arch_spin_trylock(arch_spinlock_t *lock)
 
 static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
-   __ticket_t next = lock-tickets.head + 1;
+   __ticket_t next = lock-tickets.head + TICKET_LOCK_INC;
 
-   __add(lock-tickets.head, 1, UNLOCK_LOCK_PREFIX);
+   __add(lock-tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
__ticket_unlock_kick(lock, next);
 }
 
@@ -129,7 +129,7 @@ static inline int arch_spin_is_contended(arch_spinlock_t 
*lock)
 {
struct __raw_tickets tmp = ACCESS_ONCE(lock-tickets);
 
-   return (__ticket_t)(tmp.tail - tmp.head)  1;
+   return (__ticket_t)(tmp.tail - tmp.head)  TICKET_LOCK_INC;
 }
 #define arch_spin_is_contended arch_spin_is_contended
 
diff --git a/arch/x86/include/asm/spinlock_types.h 
b/arch/x86/include/asm/spinlock_types.h
index 83fd3c7..e96fcbd 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -3,7 +3,13 @@
 
 #include linux/types.h
 
-#if (CONFIG_NR_CPUS  256)
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#define __TICKET_LOCK_INC  2
+#else
+#define __TICKET_LOCK_INC  1
+#endif
+
+#if (CONFIG_NR_CPUS  (256 / __TICKET_LOCK_INC))
 typedef u8  __ticket_t;
 typedef u16 __ticketpair_t;
 #else
@@ -11,6 +17,8 @@ typedef u16 __ticket_t;
 typedef u32 __ticketpair_t;
 #endif
 
+#define TICKET_LOCK_INC((__ticket_t)__TICKET_LOCK_INC)
+
 #define TICKET_SHIFT   (sizeof(__ticket_t) * 8)
 
 typedef struct arch_spinlock {

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