[PATCH V12 1/14] x86/spinlock: Replace pv spinlocks with pv ticketlocks

[PATCH V12 1/14] x86/spinlock: Replace pv spinlocks with pv ticketlocks

[Raghavendra K T]

x86/spinlock: Replace pv spinlocks with pv ticketlocks

From: Jeremy Fitzhardinge <jeremy@goop.org>

Rather than outright replacing the entire spinlock implementation in
order to paravirtualize it, keep the ticket lock implementation but add
a couple of pvops hooks on the slow patch (long spin on lock, unlocking
a contended lock).

Ticket locks have a number of nice properties, but they also have some
surprising behaviours in virtual environments.  They enforce a strict
FIFO ordering on cpus trying to take a lock; however, if the hypervisor
scheduler does not schedule the cpus in the correct order, the system can
waste a huge amount of time spinning until the next cpu can take the lock.

(See Thomas Friebel's talk "Prevent Guests from Spinning Around"
http://www.xen.org/files/xensummitboston08/LHP.pdf for more details.)

To address this, we add two hooks:
 - __ticket_spin_lock which is called after the cpu has been
   spinning on the lock for a significant number of iterations but has
   failed to take the lock (presumably because the cpu holding the lock
   has been descheduled).  The lock_spinning pvop is expected to block
   the cpu until it has been kicked by the current lock holder.
 - __ticket_spin_unlock, which on releasing a contended lock
   (there are more cpus with tail tickets), it looks to see if the next
   cpu is blocked and wakes it if so.

When compiled with CONFIG_PARAVIRT_SPINLOCKS disabled, a set of stub
functions causes all the extra code to go away.

Results:
=======
setup: 32 core machine with 32 vcpu KVM guest (HT off)  with 8GB RAM
base = 3.11-rc
patched = base + pvspinlock V12

+-----------------+----------------+--------+
 dbench (Throughput in MB/sec. Higher is better)
+-----------------+----------------+--------+
|   base (stdev %)|patched(stdev%) | %gain  |
+-----------------+----------------+--------+
| 15035.3   (0.3) |15150.0   (0.6) |   0.8  |
|  1470.0   (2.2) | 1713.7   (1.9) |  16.6  |
|   848.6   (4.3) |  967.8   (4.3) |  14.0  |
|   652.9   (3.5) |  685.3   (3.7) |   5.0  |
+-----------------+----------------+--------+

pvspinlock shows benefits for overcommit ratio > 1 for PLE enabled cases,
and undercommits results are flat

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Attilio Rao <attilio.rao@citrix.com>
[ Raghavendra: Changed SPIN_THRESHOLD ]
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/paravirt.h       |   32 ++++----------------
 arch/x86/include/asm/paravirt_types.h |   10 ++----
 arch/x86/include/asm/spinlock.h       |   53 +++++++++++++++++++++++++++------
 arch/x86/include/asm/spinlock_types.h |    4 --
 arch/x86/kernel/paravirt-spinlocks.c  |   15 +--------
 arch/x86/xen/spinlock.c               |    8 ++++-
 6 files changed, 61 insertions(+), 61 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index cfdc9ee..040e72d 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -712,36 +712,16 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx,
 
 #if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT_SPINLOCKS)
 
-static inline int arch_spin_is_locked(struct arch_spinlock *lock)
+static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
+							__ticket_t ticket)
 {
-	return PVOP_CALL1(int, pv_lock_ops.spin_is_locked, lock);
+	PVOP_VCALL2(pv_lock_ops.lock_spinning, lock, ticket);
 }
 
-static inline int arch_spin_is_contended(struct arch_spinlock *lock)
+static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
+							__ticket_t ticket)
 {
-	return PVOP_CALL1(int, pv_lock_ops.spin_is_contended, lock);
-}
-#define arch_spin_is_contended	arch_spin_is_contended
-
-static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
-{
-	PVOP_VCALL1(pv_lock_ops.spin_lock, lock);
-}
-
-static __always_inline void arch_spin_lock_flags(struct arch_spinlock *lock,
-						  unsigned long flags)
-{
-	PVOP_VCALL2(pv_lock_ops.spin_lock_flags, lock, flags);
-}
-
-static __always_inline int arch_spin_trylock(struct arch_spinlock *lock)
-{
-	return PVOP_CALL1(int, pv_lock_ops.spin_trylock, lock);
-}
-
-static __always_inline void arch_spin_unlock(struct arch_spinlock *lock)
-{
-	PVOP_VCALL1(pv_lock_ops.spin_unlock, lock);
+	PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
 }
 
 #endif
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 0db1fca..d5deb6d 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -327,13 +327,11 @@ struct pv_mmu_ops {
 };
 
 struct arch_spinlock;
+#include <asm/spinlock_types.h>
+
 struct pv_lock_ops {
-	int (*spin_is_locked)(struct arch_spinlock *lock);
-	int (*spin_is_contended)(struct arch_spinlock *lock);
-	void (*spin_lock)(struct arch_spinlock *lock);
-	void (*spin_lock_flags)(struct arch_spinlock *lock, unsigned long flags);
-	int (*spin_trylock)(struct arch_spinlock *lock);
-	void (*spin_unlock)(struct arch_spinlock *lock);
+	void (*lock_spinning)(struct arch_spinlock *lock, __ticket_t ticket);
+	void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
 };
 
 /* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 33692ea..4d54244 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -34,6 +34,35 @@
 # define UNLOCK_LOCK_PREFIX
 #endif
 
+/* How long a lock should spin before we consider blocking */
+#define SPIN_THRESHOLD	(1 << 15)
+
+#ifndef CONFIG_PARAVIRT_SPINLOCKS
+
+static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
+							__ticket_t ticket)
+{
+}
+
+static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
+							 __ticket_t ticket)
+{
+}
+
+#endif	/* CONFIG_PARAVIRT_SPINLOCKS */
+
+
+/*
+ * If a spinlock has someone waiting on it, then kick the appropriate
+ * waiting cpu.
+ */
+static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
+							__ticket_t next)
+{
+	if (unlikely(lock->tickets.tail != next))
+		____ticket_unlock_kick(lock, next);
+}
+
 /*
  * Ticket locks are conceptually two parts, one indicating the current head of
  * the queue, and the other indicating the current tail. The lock is acquired
@@ -47,19 +76,24 @@
  * in the high part, because a wide xadd increment of the low part would carry
  * up and contaminate the high part.
  */
-static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
+static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
 {
 	register struct __raw_tickets inc = { .tail = 1 };
 
 	inc = xadd(&lock->tickets, inc);
 
 	for (;;) {
-		if (inc.head == inc.tail)
-			break;
-		cpu_relax();
-		inc.head = ACCESS_ONCE(lock->tickets.head);
+		unsigned count = SPIN_THRESHOLD;
+
+		do {
+			if (inc.head == inc.tail)
+				goto out;
+			cpu_relax();
+			inc.head = ACCESS_ONCE(lock->tickets.head);
+		} while (--count);
+		__ticket_lock_spinning(lock, inc.tail);
 	}
-	barrier();		/* make sure nothing creeps before the lock is taken */
+out:	barrier();	/* make sure nothing creeps before the lock is taken */
 }
 
 static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
@@ -78,7 +112,10 @@ static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
 
 static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
 {
+	__ticket_t next = lock->tickets.head + 1;
+
 	__add(&lock->tickets.head, 1, UNLOCK_LOCK_PREFIX);
+	__ticket_unlock_kick(lock, next);
 }
 
 static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
@@ -95,8 +132,6 @@ static inline int __ticket_spin_is_contended(arch_spinlock_t *lock)
 	return (__ticket_t)(tmp.tail - tmp.head) > 1;
 }
 
-#ifndef CONFIG_PARAVIRT_SPINLOCKS
-
 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
 {
 	return __ticket_spin_is_locked(lock);
@@ -129,8 +164,6 @@ static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
 	arch_spin_lock(lock);
 }
 
-#endif	/* CONFIG_PARAVIRT_SPINLOCKS */
-
 static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
 {
 	while (arch_spin_is_locked(lock))
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index ad0ad07..83fd3c7 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -1,10 +1,6 @@
 #ifndef _ASM_X86_SPINLOCK_TYPES_H
 #define _ASM_X86_SPINLOCK_TYPES_H
 
-#ifndef __LINUX_SPINLOCK_TYPES_H
-# error "please don't include this file directly"
-#endif
-
 #include <linux/types.h>
 
 #if (CONFIG_NR_CPUS < 256)
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index 676b8c7..c2e010e 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -7,21 +7,10 @@
 
 #include <asm/paravirt.h>
 
-static inline void
-default_spin_lock_flags(arch_spinlock_t *lock, unsigned long flags)
-{
-	arch_spin_lock(lock);
-}
-
 struct pv_lock_ops pv_lock_ops = {
 #ifdef CONFIG_SMP
-	.spin_is_locked = __ticket_spin_is_locked,
-	.spin_is_contended = __ticket_spin_is_contended,
-
-	.spin_lock = __ticket_spin_lock,
-	.spin_lock_flags = default_spin_lock_flags,
-	.spin_trylock = __ticket_spin_trylock,
-	.spin_unlock = __ticket_spin_unlock,
+	.lock_spinning = paravirt_nop,
+	.unlock_kick = paravirt_nop,
 #endif
 };
 EXPORT_SYMBOL(pv_lock_ops);
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index cf3caee..d509629 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -139,6 +139,9 @@ struct xen_spinlock {
 	xen_spinners_t spinners;	/* count of waiting cpus */
 };
 
+static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
+
+#if 0
 static int xen_spin_is_locked(struct arch_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
@@ -167,7 +170,6 @@ static int xen_spin_trylock(struct arch_spinlock *lock)
 }
 
 static DEFINE_PER_CPU(char *, irq_name);
-static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
 static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
 
 /*
@@ -354,6 +356,7 @@ static void xen_spin_unlock(struct arch_spinlock *lock)
 	if (unlikely(xl->spinners))
 		xen_spin_unlock_slow(xl);
 }
+#endif
 
 static irqreturn_t dummy_handler(int irq, void *dev_id)
 {
@@ -418,13 +421,14 @@ void __init xen_init_spinlocks(void)
 		return;
 
 	BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));
-
+#if 0
 	pv_lock_ops.spin_is_locked = xen_spin_is_locked;
 	pv_lock_ops.spin_is_contended = xen_spin_is_contended;
 	pv_lock_ops.spin_lock = xen_spin_lock;
 	pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
 	pv_lock_ops.spin_trylock = xen_spin_trylock;
 	pv_lock_ops.spin_unlock = xen_spin_unlock;
+#endif
 }
 
 #ifdef CONFIG_XEN_DEBUG_FS

[PATCH V12 2/14] x86/ticketlock: Don't inline _spin_unlock when using paravirt spinlocks

[Raghavendra K T]

x86/ticketlock: Don't inline _spin_unlock when using paravirt spinlocks

From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>

The code size expands somewhat, and its better to just call
a function rather than inline it.

Thanks Jeremy for original version of ARCH_NOINLINE_SPIN_UNLOCK config patch,
which is simplified.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/Kconfig |    1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7f3867c..724ce55 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -663,6 +663,7 @@ config PARAVIRT_DEBUG
 config PARAVIRT_SPINLOCKS
 	bool "Paravirtualization layer for spinlocks"
 	depends on PARAVIRT && SMP
+	select UNINLINE_SPIN_UNLOCK
 	---help---
 	  Paravirtualized spinlocks allow a pvops backend to replace the
 	  spinlock implementation with something virtualization-friendly

[PATCH V12 3/14] x86/ticketlock: Collapse a layer of functions

[Raghavendra K T]

x86/ticketlock: Collapse a layer of functions

From: Jeremy Fitzhardinge <jeremy@goop.org>

Now that the paravirtualization layer doesn't exist at the spinlock
level any more, we can collapse the __ticket_ functions into the arch_
functions.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Attilio Rao <attilio.rao@citrix.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/spinlock.h |   35 +++++------------------------------
 1 file changed, 5 insertions(+), 30 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 4d54244..7442410 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -76,7 +76,7 @@ static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
  * in the high part, because a wide xadd increment of the low part would carry
  * up and contaminate the high part.
  */
-static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
+static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
 {
 	register struct __raw_tickets inc = { .tail = 1 };
 
@@ -96,7 +96,7 @@ static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
 out:	barrier();	/* make sure nothing creeps before the lock is taken */
 }
 
-static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
+static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
 {
 	arch_spinlock_t old, new;
 
@@ -110,7 +110,7 @@ static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
 	return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
 }
 
-static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
+static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
 	__ticket_t next = lock->tickets.head + 1;
 
@@ -118,46 +118,21 @@ static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
 	__ticket_unlock_kick(lock, next);
 }
 
-static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
+static inline int arch_spin_is_locked(arch_spinlock_t *lock)
 {
 	struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);
 
 	return tmp.tail != tmp.head;
 }
 
-static inline int __ticket_spin_is_contended(arch_spinlock_t *lock)
+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;
 }
-
-static inline int arch_spin_is_locked(arch_spinlock_t *lock)
-{
-	return __ticket_spin_is_locked(lock);
-}
-
-static inline int arch_spin_is_contended(arch_spinlock_t *lock)
-{
-	return __ticket_spin_is_contended(lock);
-}
 #define arch_spin_is_contended	arch_spin_is_contended
 
-static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
-{
-	__ticket_spin_lock(lock);
-}
-
-static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
-{
-	return __ticket_spin_trylock(lock);
-}
-
-static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
-{
-	__ticket_spin_unlock(lock);
-}
-
 static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
 						  unsigned long flags)
 {

[PATCH V12 4/14] xen: Defer spinlock setup until boot CPU setup

[Raghavendra K T]

xen: Defer spinlock setup until boot CPU setup

From: Jeremy Fitzhardinge <jeremy@goop.org>

There's no need to do it at very early init, and doing it there
makes it impossible to use the jump_label machinery.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/xen/smp.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index ca92754..3b52d80 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -279,6 +279,7 @@ static void __init xen_smp_prepare_boot_cpu(void)
 
 	xen_filter_cpu_maps();
 	xen_setup_vcpu_info_placement();
+	xen_init_spinlocks();
 }
 
 static void __init xen_smp_prepare_cpus(unsigned int max_cpus)
@@ -680,7 +681,6 @@ void __init xen_smp_init(void)
 {
 	smp_ops = xen_smp_ops;
 	xen_fill_possible_map();
-	xen_init_spinlocks();
 }
 
 static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)

[PATCH V12 5/14] xen/pvticketlock: Xen implementation for PV ticket locks

[Raghavendra K T]

xen/pvticketlock: Xen implementation for PV ticket locks

From: Jeremy Fitzhardinge <jeremy@goop.org>

Replace the old Xen implementation of PV spinlocks with and implementation
of xen_lock_spinning and xen_unlock_kick.

xen_lock_spinning simply registers the cpu in its entry in lock_waiting,
adds itself to the waiting_cpus set, and blocks on an event channel
until the channel becomes pending.

xen_unlock_kick searches the cpus in waiting_cpus looking for the one
which next wants this lock with the next ticket, if any.  If found,
it kicks it by making its event channel pending, which wakes it up.

We need to make sure interrupts are disabled while we're relying on the
contents of the per-cpu lock_waiting values, otherwise an interrupt
handler could come in, try to take some other lock, block, and overwrite
our values.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 [ Raghavendra:  use function + enum instead of macro, cmpxchg for zero status reset
Reintroduce break since we know the exact vCPU to send IPI as suggested by Konrad.]
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/xen/spinlock.c |  348 +++++++++++------------------------------------
 1 file changed, 79 insertions(+), 269 deletions(-)

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index d509629..a458729 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -17,45 +17,44 @@
 #include "xen-ops.h"
 #include "debugfs.h"
 
-#ifdef CONFIG_XEN_DEBUG_FS
-static struct xen_spinlock_stats
-{
-	u64 taken;
-	u32 taken_slow;
-	u32 taken_slow_nested;
-	u32 taken_slow_pickup;
-	u32 taken_slow_spurious;
-	u32 taken_slow_irqenable;
+enum xen_contention_stat {
+	TAKEN_SLOW,
+	TAKEN_SLOW_PICKUP,
+	TAKEN_SLOW_SPURIOUS,
+	RELEASED_SLOW,
+	RELEASED_SLOW_KICKED,
+	NR_CONTENTION_STATS
+};
 
-	u64 released;
-	u32 released_slow;
-	u32 released_slow_kicked;
 
+#ifdef CONFIG_XEN_DEBUG_FS
 #define HISTO_BUCKETS	30
-	u32 histo_spin_total[HISTO_BUCKETS+1];
-	u32 histo_spin_spinning[HISTO_BUCKETS+1];
+static struct xen_spinlock_stats
+{
+	u32 contention_stats[NR_CONTENTION_STATS];
 	u32 histo_spin_blocked[HISTO_BUCKETS+1];
-
-	u64 time_total;
-	u64 time_spinning;
 	u64 time_blocked;
 } spinlock_stats;
 
 static u8 zero_stats;
 
-static unsigned lock_timeout = 1 << 10;
-#define TIMEOUT lock_timeout
-
 static inline void check_zero(void)
 {
-	if (unlikely(zero_stats)) {
-		memset(&spinlock_stats, 0, sizeof(spinlock_stats));
-		zero_stats = 0;
+	u8 ret;
+	u8 old = ACCESS_ONCE(zero_stats);
+	if (unlikely(old)) {
+		ret = cmpxchg(&zero_stats, old, 0);
+		/* This ensures only one fellow resets the stat */
+		if (ret == old)
+			memset(&spinlock_stats, 0, sizeof(spinlock_stats));
 	}
 }
 
-#define ADD_STATS(elem, val)			\
-	do { check_zero(); spinlock_stats.elem += (val); } while(0)
+static inline void add_stats(enum xen_contention_stat var, u32 val)
+{
+	check_zero();
+	spinlock_stats.contention_stats[var] += val;
+}
 
 static inline u64 spin_time_start(void)
 {
@@ -74,22 +73,6 @@ static void __spin_time_accum(u64 delta, u32 *array)
 		array[HISTO_BUCKETS]++;
 }
 
-static inline void spin_time_accum_spinning(u64 start)
-{
-	u32 delta = xen_clocksource_read() - start;
-
-	__spin_time_accum(delta, spinlock_stats.histo_spin_spinning);
-	spinlock_stats.time_spinning += delta;
-}
-
-static inline void spin_time_accum_total(u64 start)
-{
-	u32 delta = xen_clocksource_read() - start;
-
-	__spin_time_accum(delta, spinlock_stats.histo_spin_total);
-	spinlock_stats.time_total += delta;
-}
-
 static inline void spin_time_accum_blocked(u64 start)
 {
 	u32 delta = xen_clocksource_read() - start;
@@ -99,19 +82,15 @@ static inline void spin_time_accum_blocked(u64 start)
 }
 #else  /* !CONFIG_XEN_DEBUG_FS */
 #define TIMEOUT			(1 << 10)
-#define ADD_STATS(elem, val)	do { (void)(val); } while(0)
+static inline void add_stats(enum xen_contention_stat var, u32 val)
+{
+}
 
 static inline u64 spin_time_start(void)
 {
 	return 0;
 }
 
-static inline void spin_time_accum_total(u64 start)
-{
-}
-static inline void spin_time_accum_spinning(u64 start)
-{
-}
 static inline void spin_time_accum_blocked(u64 start)
 {
 }
@@ -134,230 +113,84 @@ typedef u16 xen_spinners_t;
 	asm(LOCK_PREFIX " decw %0" : "+m" ((xl)->spinners) : : "memory");
 #endif
 
-struct xen_spinlock {
-	unsigned char lock;		/* 0 -> free; 1 -> locked */
-	xen_spinners_t spinners;	/* count of waiting cpus */
+struct xen_lock_waiting {
+	struct arch_spinlock *lock;
+	__ticket_t want;
 };
 
 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
-
-#if 0
-static int xen_spin_is_locked(struct arch_spinlock *lock)
-{
-	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-
-	return xl->lock != 0;
-}
-
-static int xen_spin_is_contended(struct arch_spinlock *lock)
-{
-	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-
-	/* Not strictly true; this is only the count of contended
-	   lock-takers entering the slow path. */
-	return xl->spinners != 0;
-}
-
-static int xen_spin_trylock(struct arch_spinlock *lock)
-{
-	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-	u8 old = 1;
-
-	asm("xchgb %b0,%1"
-	    : "+q" (old), "+m" (xl->lock) : : "memory");
-
-	return old == 0;
-}
-
 static DEFINE_PER_CPU(char *, irq_name);
-static DEFINE_PER_CPU(struct xen_spinlock *, lock_spinners);
+static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
+static cpumask_t waiting_cpus;
 
-/*
- * Mark a cpu as interested in a lock.  Returns the CPU's previous
- * lock of interest, in case we got preempted by an interrupt.
- */
-static inline struct xen_spinlock *spinning_lock(struct xen_spinlock *xl)
+static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 {
-	struct xen_spinlock *prev;
-
-	prev = __this_cpu_read(lock_spinners);
-	__this_cpu_write(lock_spinners, xl);
-
-	wmb();			/* set lock of interest before count */
-
-	inc_spinners(xl);
-
-	return prev;
-}
-
-/*
- * Mark a cpu as no longer interested in a lock.  Restores previous
- * lock of interest (NULL for none).
- */
-static inline void unspinning_lock(struct xen_spinlock *xl, struct xen_spinlock *prev)
-{
-	dec_spinners(xl);
-	wmb();			/* decrement count before restoring lock */
-	__this_cpu_write(lock_spinners, prev);
-}
-
-static noinline int xen_spin_lock_slow(struct arch_spinlock *lock, bool irq_enable)
-{
-	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-	struct xen_spinlock *prev;
 	int irq = __this_cpu_read(lock_kicker_irq);
-	int ret;
+	struct xen_lock_waiting *w = &__get_cpu_var(lock_waiting);
+	int cpu = smp_processor_id();
 	u64 start;
+	unsigned long flags;
 
 	/* If kicker interrupts not initialized yet, just spin */
 	if (irq == -1)
-		return 0;
+		return;
 
 	start = spin_time_start();
 
-	/* announce we're spinning */
-	prev = spinning_lock(xl);
-
-	ADD_STATS(taken_slow, 1);
-	ADD_STATS(taken_slow_nested, prev != NULL);
-
-	do {
-		unsigned long flags;
-
-		/* clear pending */
-		xen_clear_irq_pending(irq);
-
-		/* check again make sure it didn't become free while
-		   we weren't looking  */
-		ret = xen_spin_trylock(lock);
-		if (ret) {
-			ADD_STATS(taken_slow_pickup, 1);
-
-			/*
-			 * If we interrupted another spinlock while it
-			 * was blocking, make sure it doesn't block
-			 * without rechecking the lock.
-			 */
-			if (prev != NULL)
-				xen_set_irq_pending(irq);
-			goto out;
-		}
+	/*
+	 * Make sure an interrupt handler can't upset things in a
+	 * partially setup state.
+	 */
+	local_irq_save(flags);
 
-		flags = arch_local_save_flags();
-		if (irq_enable) {
-			ADD_STATS(taken_slow_irqenable, 1);
-			raw_local_irq_enable();
-		}
+	w->want = want;
+	smp_wmb();
+	w->lock = lock;
 
-		/*
-		 * Block until irq becomes pending.  If we're
-		 * interrupted at this point (after the trylock but
-		 * before entering the block), then the nested lock
-		 * handler guarantees that the irq will be left
-		 * pending if there's any chance the lock became free;
-		 * xen_poll_irq() returns immediately if the irq is
-		 * pending.
-		 */
-		xen_poll_irq(irq);
+	/* This uses set_bit, which atomic and therefore a barrier */
+	cpumask_set_cpu(cpu, &waiting_cpus);
+	add_stats(TAKEN_SLOW, 1);
 
-		raw_local_irq_restore(flags);
+	/* clear pending */
+	xen_clear_irq_pending(irq);
 
-		ADD_STATS(taken_slow_spurious, !xen_test_irq_pending(irq));
-	} while (!xen_test_irq_pending(irq)); /* check for spurious wakeups */
+	/* Only check lock once pending cleared */
+	barrier();
 
+	/* check again make sure it didn't become free while
+	   we weren't looking  */
+	if (ACCESS_ONCE(lock->tickets.head) == want) {
+		add_stats(TAKEN_SLOW_PICKUP, 1);
+		goto out;
+	}
+	/* Block until irq becomes pending (or perhaps a spurious wakeup) */
+	xen_poll_irq(irq);
+	add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
 	kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
-
 out:
-	unspinning_lock(xl, prev);
+	cpumask_clear_cpu(cpu, &waiting_cpus);
+	w->lock = NULL;
+	local_irq_restore(flags);
 	spin_time_accum_blocked(start);
-
-	return ret;
 }
 
-static inline void __xen_spin_lock(struct arch_spinlock *lock, bool irq_enable)
-{
-	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-	unsigned timeout;
-	u8 oldval;
-	u64 start_spin;
-
-	ADD_STATS(taken, 1);
-
-	start_spin = spin_time_start();
-
-	do {
-		u64 start_spin_fast = spin_time_start();
-
-		timeout = TIMEOUT;
-
-		asm("1: xchgb %1,%0\n"
-		    "   testb %1,%1\n"
-		    "   jz 3f\n"
-		    "2: rep;nop\n"
-		    "   cmpb $0,%0\n"
-		    "   je 1b\n"
-		    "   dec %2\n"
-		    "   jnz 2b\n"
-		    "3:\n"
-		    : "+m" (xl->lock), "=q" (oldval), "+r" (timeout)
-		    : "1" (1)
-		    : "memory");
-
-		spin_time_accum_spinning(start_spin_fast);
-
-	} while (unlikely(oldval != 0 &&
-			  (TIMEOUT == ~0 || !xen_spin_lock_slow(lock, irq_enable))));
-
-	spin_time_accum_total(start_spin);
-}
-
-static void xen_spin_lock(struct arch_spinlock *lock)
-{
-	__xen_spin_lock(lock, false);
-}
-
-static void xen_spin_lock_flags(struct arch_spinlock *lock, unsigned long flags)
-{
-	__xen_spin_lock(lock, !raw_irqs_disabled_flags(flags));
-}
-
-static noinline void xen_spin_unlock_slow(struct xen_spinlock *xl)
+static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
 {
 	int cpu;
 
-	ADD_STATS(released_slow, 1);
+	add_stats(RELEASED_SLOW, 1);
+
+	for_each_cpu(cpu, &waiting_cpus) {
+		const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
 
-	for_each_online_cpu(cpu) {
-		/* XXX should mix up next cpu selection */
-		if (per_cpu(lock_spinners, cpu) == xl) {
-			ADD_STATS(released_slow_kicked, 1);
+		if (w->lock == lock && w->want == next) {
+			add_stats(RELEASED_SLOW_KICKED, 1);
 			xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
+			break;
 		}
 	}
 }
 
-static void xen_spin_unlock(struct arch_spinlock *lock)
-{
-	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
-
-	ADD_STATS(released, 1);
-
-	smp_wmb();		/* make sure no writes get moved after unlock */
-	xl->lock = 0;		/* release lock */
-
-	/*
-	 * Make sure unlock happens before checking for waiting
-	 * spinners.  We need a strong barrier to enforce the
-	 * write-read ordering to different memory locations, as the
-	 * CPU makes no implied guarantees about their ordering.
-	 */
-	mb();
-
-	if (unlikely(xl->spinners))
-		xen_spin_unlock_slow(xl);
-}
-#endif
-
 static irqreturn_t dummy_handler(int irq, void *dev_id)
 {
 	BUG();
@@ -420,15 +253,8 @@ void __init xen_init_spinlocks(void)
 	if (xen_hvm_domain())
 		return;
 
-	BUILD_BUG_ON(sizeof(struct xen_spinlock) > sizeof(arch_spinlock_t));
-#if 0
-	pv_lock_ops.spin_is_locked = xen_spin_is_locked;
-	pv_lock_ops.spin_is_contended = xen_spin_is_contended;
-	pv_lock_ops.spin_lock = xen_spin_lock;
-	pv_lock_ops.spin_lock_flags = xen_spin_lock_flags;
-	pv_lock_ops.spin_trylock = xen_spin_trylock;
-	pv_lock_ops.spin_unlock = xen_spin_unlock;
-#endif
+	pv_lock_ops.lock_spinning = xen_lock_spinning;
+	pv_lock_ops.unlock_kick = xen_unlock_kick;
 }
 
 #ifdef CONFIG_XEN_DEBUG_FS
@@ -446,37 +272,21 @@ static int __init xen_spinlock_debugfs(void)
 
 	debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
 
-	debugfs_create_u32("timeout", 0644, d_spin_debug, &lock_timeout);
-
-	debugfs_create_u64("taken", 0444, d_spin_debug, &spinlock_stats.taken);
 	debugfs_create_u32("taken_slow", 0444, d_spin_debug,
-			   &spinlock_stats.taken_slow);
-	debugfs_create_u32("taken_slow_nested", 0444, d_spin_debug,
-			   &spinlock_stats.taken_slow_nested);
+			   &spinlock_stats.contention_stats[TAKEN_SLOW]);
 	debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
-			   &spinlock_stats.taken_slow_pickup);
+			   &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
 	debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
-			   &spinlock_stats.taken_slow_spurious);
-	debugfs_create_u32("taken_slow_irqenable", 0444, d_spin_debug,
-			   &spinlock_stats.taken_slow_irqenable);
+			   &spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
 
-	debugfs_create_u64("released", 0444, d_spin_debug, &spinlock_stats.released);
 	debugfs_create_u32("released_slow", 0444, d_spin_debug,
-			   &spinlock_stats.released_slow);
+			   &spinlock_stats.contention_stats[RELEASED_SLOW]);
 	debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
-			   &spinlock_stats.released_slow_kicked);
+			   &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
 
-	debugfs_create_u64("time_spinning", 0444, d_spin_debug,
-			   &spinlock_stats.time_spinning);
 	debugfs_create_u64("time_blocked", 0444, d_spin_debug,
 			   &spinlock_stats.time_blocked);
-	debugfs_create_u64("time_total", 0444, d_spin_debug,
-			   &spinlock_stats.time_total);
 
-	debugfs_create_u32_array("histo_total", 0444, d_spin_debug,
-				spinlock_stats.histo_spin_total, HISTO_BUCKETS + 1);
-	debugfs_create_u32_array("histo_spinning", 0444, d_spin_debug,
-				spinlock_stats.histo_spin_spinning, HISTO_BUCKETS + 1);
 	debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
 				spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);

[PATCH V12 6/14] xen/pvticketlocks: Add xen_nopvspin parameter to disable xen pv ticketlocks

[Raghavendra K T]

xen/pvticketlocks: Add xen_nopvspin parameter to disable xen pv ticketlocks

From: Jeremy Fitzhardinge <jeremy@goop.org>

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/xen/spinlock.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index a458729..669a971 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -244,6 +244,8 @@ void xen_uninit_lock_cpu(int cpu)
 	per_cpu(irq_name, cpu) = NULL;
 }
 
+static bool xen_pvspin __initdata = true;
+
 void __init xen_init_spinlocks(void)
 {
 	/*
@@ -253,10 +255,22 @@ void __init xen_init_spinlocks(void)
 	if (xen_hvm_domain())
 		return;
 
+	if (!xen_pvspin) {
+		printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
+		return;
+	}
+
 	pv_lock_ops.lock_spinning = xen_lock_spinning;
 	pv_lock_ops.unlock_kick = xen_unlock_kick;
 }
 
+static __init int xen_parse_nopvspin(char *arg)
+{
+	xen_pvspin = false;
+	return 0;
+}
+early_param("xen_nopvspin", xen_parse_nopvspin);
+
 #ifdef CONFIG_XEN_DEBUG_FS
 
 static struct dentry *d_spin_debug;

[PATCH V12 7/14] x86/pvticketlock: Use callee-save for lock_spinning

[Raghavendra K T]

x86/pvticketlock: Use callee-save for lock_spinning

From: Jeremy Fitzhardinge <jeremy@goop.org>

Although the lock_spinning calls in the spinlock code are on the
uncommon path, their presence can cause the compiler to generate many
more register save/restores in the function pre/postamble, which is in
the fast path.  To avoid this, convert it to using the pvops callee-save
calling convention, which defers all the save/restores until the actual
function is called, keeping the fastpath clean.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Attilio Rao <attilio.rao@citrix.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/paravirt.h       |    2 +-
 arch/x86/include/asm/paravirt_types.h |    2 +-
 arch/x86/kernel/paravirt-spinlocks.c  |    2 +-
 arch/x86/xen/spinlock.c               |    3 ++-
 4 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 040e72d..7131e12c 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -715,7 +715,7 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx,
 static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
 							__ticket_t ticket)
 {
-	PVOP_VCALL2(pv_lock_ops.lock_spinning, lock, ticket);
+	PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
 }
 
 static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index d5deb6d..350d017 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -330,7 +330,7 @@ struct arch_spinlock;
 #include <asm/spinlock_types.h>
 
 struct pv_lock_ops {
-	void (*lock_spinning)(struct arch_spinlock *lock, __ticket_t ticket);
+	struct paravirt_callee_save lock_spinning;
 	void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
 };
 
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index c2e010e..4251c1d 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -9,7 +9,7 @@
 
 struct pv_lock_ops pv_lock_ops = {
 #ifdef CONFIG_SMP
-	.lock_spinning = paravirt_nop,
+	.lock_spinning = __PV_IS_CALLEE_SAVE(paravirt_nop),
 	.unlock_kick = paravirt_nop,
 #endif
 };
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 669a971..6c8792b 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -173,6 +173,7 @@ out:
 	local_irq_restore(flags);
 	spin_time_accum_blocked(start);
 }
+PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
 
 static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
 {
@@ -260,7 +261,7 @@ void __init xen_init_spinlocks(void)
 		return;
 	}
 
-	pv_lock_ops.lock_spinning = xen_lock_spinning;
+	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
 	pv_lock_ops.unlock_kick = xen_unlock_kick;
 }

[PATCH V12 8/14] x86/pvticketlock: When paravirtualizing ticket locks, increment by 2

[Raghavendra K T]

x86/pvticketlock: When paravirtualizing ticket locks, increment by 2

From: Jeremy Fitzhardinge <jeremy@goop.org>

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@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Tested-by: Attilio Rao <attilio.rao@citrix.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 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 {

[PATCH V12 9/14] jump_label: Split out rate limiting from jump_label.h

[Raghavendra K T]

jump_label: Split jumplabel ratelimit

From: Andrew Jones <drjones@redhat.com>

Commit b202952075f62603bea9bfb6ebc6b0420db11949 ("perf, core: Rate limit
perf_sched_events jump_label patching") introduced rate limiting
for jump label disabling. The changes were made in the jump label code
in order to be more widely available and to keep things tidier. This is
all fine, except now jump_label.h includes linux/workqueue.h, which
makes it impossible to include jump_label.h from anything that
workqueue.h needs. For example, it's now impossible to include
jump_label.h from asm/spinlock.h, which is done in proposed
pv-ticketlock patches. This patch splits out the rate limiting related
changes from jump_label.h into a new file, jump_label_ratelimit.h, to
resolve the issue.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 include/linux/jump_label.h           |   26 +-------------------------
 include/linux/jump_label_ratelimit.h |   34 ++++++++++++++++++++++++++++++++++
 include/linux/perf_event.h           |    1 +
 kernel/jump_label.c                  |    1 +
 4 files changed, 37 insertions(+), 25 deletions(-)
 create mode 100644 include/linux/jump_label_ratelimit.h

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 0976fc4..53cdf89 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -48,7 +48,6 @@
 
 #include <linux/types.h>
 #include <linux/compiler.h>
-#include <linux/workqueue.h>
 
 #if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
 
@@ -61,12 +60,6 @@ struct static_key {
 #endif
 };
 
-struct static_key_deferred {
-	struct static_key key;
-	unsigned long timeout;
-	struct delayed_work work;
-};
-
 # include <asm/jump_label.h>
 # define HAVE_JUMP_LABEL
 #endif	/* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */
@@ -119,10 +112,7 @@ extern void arch_jump_label_transform_static(struct jump_entry *entry,
 extern int jump_label_text_reserved(void *start, void *end);
 extern void static_key_slow_inc(struct static_key *key);
 extern void static_key_slow_dec(struct static_key *key);
-extern void static_key_slow_dec_deferred(struct static_key_deferred *key);
 extern void jump_label_apply_nops(struct module *mod);
-extern void
-jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl);
 
 #define STATIC_KEY_INIT_TRUE ((struct static_key) \
 	{ .enabled = ATOMIC_INIT(1), .entries = (void *)1 })
@@ -141,10 +131,6 @@ static __always_inline void jump_label_init(void)
 {
 }
 
-struct static_key_deferred {
-	struct static_key  key;
-};
-
 static __always_inline bool static_key_false(struct static_key *key)
 {
 	if (unlikely(atomic_read(&key->enabled)) > 0)
@@ -169,11 +155,6 @@ static inline void static_key_slow_dec(struct static_key *key)
 	atomic_dec(&key->enabled);
 }
 
-static inline void static_key_slow_dec_deferred(struct static_key_deferred *key)
-{
-	static_key_slow_dec(&key->key);
-}
-
 static inline int jump_label_text_reserved(void *start, void *end)
 {
 	return 0;
@@ -187,12 +168,6 @@ static inline int jump_label_apply_nops(struct module *mod)
 	return 0;
 }
 
-static inline void
-jump_label_rate_limit(struct static_key_deferred *key,
-		unsigned long rl)
-{
-}
-
 #define STATIC_KEY_INIT_TRUE ((struct static_key) \
 		{ .enabled = ATOMIC_INIT(1) })
 #define STATIC_KEY_INIT_FALSE ((struct static_key) \
@@ -203,6 +178,7 @@ jump_label_rate_limit(struct static_key_deferred *key,
 #define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
 #define jump_label_enabled static_key_enabled
 
+static inline int atomic_read(const atomic_t *v);
 static inline bool static_key_enabled(struct static_key *key)
 {
 	return (atomic_read(&key->enabled) > 0);
diff --git a/include/linux/jump_label_ratelimit.h b/include/linux/jump_label_ratelimit.h
new file mode 100644
index 0000000..1137883
--- /dev/null
+++ b/include/linux/jump_label_ratelimit.h
@@ -0,0 +1,34 @@
+#ifndef _LINUX_JUMP_LABEL_RATELIMIT_H
+#define _LINUX_JUMP_LABEL_RATELIMIT_H
+
+#include <linux/jump_label.h>
+#include <linux/workqueue.h>
+
+#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
+struct static_key_deferred {
+	struct static_key key;
+	unsigned long timeout;
+	struct delayed_work work;
+};
+#endif
+
+#ifdef HAVE_JUMP_LABEL
+extern void static_key_slow_dec_deferred(struct static_key_deferred *key);
+extern void
+jump_label_rate_limit(struct static_key_deferred *key, unsigned long rl);
+
+#else	/* !HAVE_JUMP_LABEL */
+struct static_key_deferred {
+	struct static_key  key;
+};
+static inline void static_key_slow_dec_deferred(struct static_key_deferred *key)
+{
+	static_key_slow_dec(&key->key);
+}
+static inline void
+jump_label_rate_limit(struct static_key_deferred *key,
+		unsigned long rl)
+{
+}
+#endif	/* HAVE_JUMP_LABEL */
+#endif	/* _LINUX_JUMP_LABEL_RATELIMIT_H */
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c43f6ea..226be8d 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -48,6 +48,7 @@ struct perf_guest_info_callbacks {
 #include <linux/cpu.h>
 #include <linux/irq_work.h>
 #include <linux/static_key.h>
+#include <linux/jump_label_ratelimit.h>
 #include <linux/atomic.h>
 #include <linux/sysfs.h>
 #include <linux/perf_regs.h>
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 60f48fa..297a924 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -13,6 +13,7 @@
 #include <linux/sort.h>
 #include <linux/err.h>
 #include <linux/static_key.h>
+#include <linux/jump_label_ratelimit.h>
 
 #ifdef HAVE_JUMP_LABEL

[PATCH V12 10/14] x86/ticketlock: Add slowpath logic

[Raghavendra K T]

x86/ticketlock: Add slowpath logic

From: Jeremy Fitzhardinge <jeremy@goop.org>

Maintain a flag in the LSB of the ticket lock tail which indicates
whether anyone is in the lock slowpath and may need kicking when
the current holder unlocks.  The flags are set when the first locker
enters the slowpath, and cleared when unlocking to an empty queue (ie,
no contention).

In the specific implementation of lock_spinning(), make sure to set
the slowpath flags on the lock just before blocking.  We must do
this before the last-chance pickup test to prevent a deadlock
with the unlocker:

Unlocker			Locker
				test for lock pickup
					-> fail
unlock
test slowpath
	-> false
				set slowpath flags
				block

Whereas this works in any ordering:

Unlocker			Locker
				set slowpath flags
				test for lock pickup
					-> fail
				block
unlock
test slowpath
	-> true, kick

If the unlocker finds that the lock has the slowpath flag set but it is
actually uncontended (ie, head == tail, so nobody is waiting), then it
clears the slowpath flag.

The unlock code uses a locked add to update the head counter.  This also
acts as a full memory barrier so that its safe to subsequently
read back the slowflag state, knowing that the updated lock is visible
to the other CPUs.  If it were an unlocked add, then the flag read may
just be forwarded from the store buffer before it was visible to the other
CPUs, which could result in a deadlock.

Unfortunately this means we need to do a locked instruction when
unlocking with PV ticketlocks.  However, if PV ticketlocks are not
enabled, then the old non-locked "add" is the only unlocking code.

Note: this code relies on gcc making sure that unlikely() code is out of
line of the fastpath, which only happens when OPTIMIZE_SIZE=n.  If it
doesn't the generated code isn't too bad, but its definitely suboptimal.

Thanks to Srivatsa Vaddagiri for providing a bugfix to the original
version of this change, which has been folded in.
Thanks to Stephan Diestelhorst for commenting on some code which relied
on an inaccurate reading of the x86 memory ordering rules.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Stephan Diestelhorst <stephan.diestelhorst@amd.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/paravirt.h       |    2 -
 arch/x86/include/asm/spinlock.h       |   86 ++++++++++++++++++++++++---------
 arch/x86/include/asm/spinlock_types.h |    2 +
 arch/x86/kernel/paravirt-spinlocks.c  |    3 +
 arch/x86/xen/spinlock.c               |    6 ++
 5 files changed, 74 insertions(+), 25 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 7131e12c..401f350 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -718,7 +718,7 @@ static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
 	PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
 }
 
-static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
+static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
 							__ticket_t ticket)
 {
 	PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 04a5cd5..d68883d 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -1,11 +1,14 @@
 #ifndef _ASM_X86_SPINLOCK_H
 #define _ASM_X86_SPINLOCK_H
 
+#include <linux/jump_label.h>
 #include <linux/atomic.h>
 #include <asm/page.h>
 #include <asm/processor.h>
 #include <linux/compiler.h>
 #include <asm/paravirt.h>
+#include <asm/bitops.h>
+
 /*
  * Your basic SMP spinlocks, allowing only a single CPU anywhere
  *
@@ -37,32 +40,28 @@
 /* How long a lock should spin before we consider blocking */
 #define SPIN_THRESHOLD	(1 << 15)
 
-#ifndef CONFIG_PARAVIRT_SPINLOCKS
+extern struct static_key paravirt_ticketlocks_enabled;
+static __always_inline bool static_key_false(struct static_key *key);
 
-static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
-							__ticket_t ticket)
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
 {
+	set_bit(0, (volatile unsigned long *)&lock->tickets.tail);
 }
 
-static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
-							 __ticket_t ticket)
+#else  /* !CONFIG_PARAVIRT_SPINLOCKS */
+static __always_inline void __ticket_lock_spinning(arch_spinlock_t *lock,
+							__ticket_t ticket)
 {
 }
-
-#endif	/* CONFIG_PARAVIRT_SPINLOCKS */
-
-
-/*
- * If a spinlock has someone waiting on it, then kick the appropriate
- * waiting cpu.
- */
-static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
-							__ticket_t next)
+static inline void __ticket_unlock_kick(arch_spinlock_t *lock,
+							__ticket_t ticket)
 {
-	if (unlikely(lock->tickets.tail != next))
-		____ticket_unlock_kick(lock, next);
 }
 
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+
 /*
  * Ticket locks are conceptually two parts, one indicating the current head of
  * the queue, and the other indicating the current tail. The lock is acquired
@@ -76,20 +75,22 @@ static __always_inline void __ticket_unlock_kick(struct arch_spinlock *lock,
  * in the high part, because a wide xadd increment of the low part would carry
  * up and contaminate the high part.
  */
-static __always_inline void arch_spin_lock(struct arch_spinlock *lock)
+static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
 {
 	register struct __raw_tickets inc = { .tail = TICKET_LOCK_INC };
 
 	inc = xadd(&lock->tickets, inc);
+	if (likely(inc.head == inc.tail))
+		goto out;
 
+	inc.tail &= ~TICKET_SLOWPATH_FLAG;
 	for (;;) {
 		unsigned count = SPIN_THRESHOLD;
 
 		do {
-			if (inc.head == inc.tail)
+			if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
 				goto out;
 			cpu_relax();
-			inc.head = ACCESS_ONCE(lock->tickets.head);
 		} while (--count);
 		__ticket_lock_spinning(lock, inc.tail);
 	}
@@ -101,7 +102,7 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
 	arch_spinlock_t old, new;
 
 	old.tickets = ACCESS_ONCE(lock->tickets);
-	if (old.tickets.head != old.tickets.tail)
+	if (old.tickets.head != (old.tickets.tail & ~TICKET_SLOWPATH_FLAG))
 		return 0;
 
 	new.head_tail = old.head_tail + (TICKET_LOCK_INC << TICKET_SHIFT);
@@ -110,12 +111,49 @@ static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
 	return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
 }
 
+static inline void __ticket_unlock_slowpath(arch_spinlock_t *lock,
+					    arch_spinlock_t old)
+{
+	arch_spinlock_t new;
+
+	BUILD_BUG_ON(((__ticket_t)NR_CPUS) != NR_CPUS);
+
+	/* Perform the unlock on the "before" copy */
+	old.tickets.head += TICKET_LOCK_INC;
+
+	/* Clear the slowpath flag */
+	new.head_tail = old.head_tail & ~(TICKET_SLOWPATH_FLAG << TICKET_SHIFT);
+
+	/*
+	 * If the lock is uncontended, clear the flag - use cmpxchg in
+	 * case it changes behind our back though.
+	 */
+	if (new.tickets.head != new.tickets.tail ||
+	    cmpxchg(&lock->head_tail, old.head_tail,
+					new.head_tail) != old.head_tail) {
+		/*
+		 * Lock still has someone queued for it, so wake up an
+		 * appropriate waiter.
+		 */
+		__ticket_unlock_kick(lock, old.tickets.head);
+	}
+}
+
 static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
 {
-	__ticket_t next = lock->tickets.head + TICKET_LOCK_INC;
+	if (TICKET_SLOWPATH_FLAG &&
+	    static_key_false(&paravirt_ticketlocks_enabled)) {
+		arch_spinlock_t prev;
+
+		prev = *lock;
+		add_smp(&lock->tickets.head, TICKET_LOCK_INC);
+
+		/* add_smp() is a full mb() */
 
-	__add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
-	__ticket_unlock_kick(lock, next);
+		if (unlikely(lock->tickets.tail & TICKET_SLOWPATH_FLAG))
+			__ticket_unlock_slowpath(lock, prev);
+	} else
+		__add(&lock->tickets.head, TICKET_LOCK_INC, UNLOCK_LOCK_PREFIX);
 }
 
 static inline int arch_spin_is_locked(arch_spinlock_t *lock)
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index e96fcbd..4f1bea1 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -5,8 +5,10 @@
 
 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 #define __TICKET_LOCK_INC	2
+#define TICKET_SLOWPATH_FLAG	((__ticket_t)1)
 #else
 #define __TICKET_LOCK_INC	1
+#define TICKET_SLOWPATH_FLAG	((__ticket_t)0)
 #endif
 
 #if (CONFIG_NR_CPUS < (256 / __TICKET_LOCK_INC))
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index 4251c1d..bbb6c73 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -4,6 +4,7 @@
  */
 #include <linux/spinlock.h>
 #include <linux/module.h>
+#include <linux/jump_label.h>
 
 #include <asm/paravirt.h>
 
@@ -15,3 +16,5 @@ struct pv_lock_ops pv_lock_ops = {
 };
 EXPORT_SYMBOL(pv_lock_ops);
 
+struct static_key paravirt_ticketlocks_enabled = STATIC_KEY_INIT_FALSE;
+EXPORT_SYMBOL(paravirt_ticketlocks_enabled);
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 6c8792b..546112e 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -157,6 +157,10 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 	/* Only check lock once pending cleared */
 	barrier();
 
+	/* Mark entry to slowpath before doing the pickup test to make
+	   sure we don't deadlock with an unlocker. */
+	__ticket_enter_slowpath(lock);
+
 	/* check again make sure it didn't become free while
 	   we weren't looking  */
 	if (ACCESS_ONCE(lock->tickets.head) == want) {
@@ -261,6 +265,8 @@ void __init xen_init_spinlocks(void)
 		return;
 	}
 
+	static_key_slow_inc(&paravirt_ticketlocks_enabled);
+
 	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
 	pv_lock_ops.unlock_kick = xen_unlock_kick;
 }

[PATCH V12 11/14] xen/pvticketlock: Allow interrupts to be enabled while blocking

[Raghavendra K T]

xen/pvticketlock: Allow interrupts to be enabled while blocking

From: Jeremy Fitzhardinge <jeremy@goop.org>

If interrupts were enabled when taking the spinlock, we can leave them
enabled while blocking to get the lock.

If we can enable interrupts while waiting for the lock to become
available, and we take an interrupt before entering the poll,
and the handler takes a spinlock which ends up going into
the slow state (invalidating the per-cpu "lock" and "want" values),
then when the interrupt handler returns the event channel will
remain pending so the poll will return immediately, causing it to
return out to the main spinlock loop.

Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/xen/spinlock.c |   46 ++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 40 insertions(+), 6 deletions(-)

diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 546112e..0438b93 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -142,7 +142,20 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 	 * partially setup state.
 	 */
 	local_irq_save(flags);
-
+	/*
+	 * We don't really care if we're overwriting some other
+	 * (lock,want) pair, as that would mean that we're currently
+	 * in an interrupt context, and the outer context had
+	 * interrupts enabled.  That has already kicked the VCPU out
+	 * of xen_poll_irq(), so it will just return spuriously and
+	 * retry with newly setup (lock,want).
+	 *
+	 * The ordering protocol on this is that the "lock" pointer
+	 * may only be set non-NULL if the "want" ticket is correct.
+	 * If we're updating "want", we must first clear "lock".
+	 */
+	w->lock = NULL;
+	smp_wmb();
 	w->want = want;
 	smp_wmb();
 	w->lock = lock;
@@ -157,24 +170,43 @@ static void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
 	/* Only check lock once pending cleared */
 	barrier();
 
-	/* Mark entry to slowpath before doing the pickup test to make
-	   sure we don't deadlock with an unlocker. */
+	/*
+	 * Mark entry to slowpath before doing the pickup test to make
+	 * sure we don't deadlock with an unlocker.
+	 */
 	__ticket_enter_slowpath(lock);
 
-	/* check again make sure it didn't become free while
-	   we weren't looking  */
+	/*
+	 * check again make sure it didn't become free while
+	 * we weren't looking
+	 */
 	if (ACCESS_ONCE(lock->tickets.head) == want) {
 		add_stats(TAKEN_SLOW_PICKUP, 1);
 		goto out;
 	}
+
+	/* Allow interrupts while blocked */
+	local_irq_restore(flags);
+
+	/*
+	 * If an interrupt happens here, it will leave the wakeup irq
+	 * pending, which will cause xen_poll_irq() to return
+	 * immediately.
+	 */
+
 	/* Block until irq becomes pending (or perhaps a spurious wakeup) */
 	xen_poll_irq(irq);
 	add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
+
+	local_irq_save(flags);
+
 	kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
 out:
 	cpumask_clear_cpu(cpu, &waiting_cpus);
 	w->lock = NULL;
+
 	local_irq_restore(flags);
+
 	spin_time_accum_blocked(start);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
@@ -188,7 +220,9 @@ static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
 	for_each_cpu(cpu, &waiting_cpus) {
 		const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
 
-		if (w->lock == lock && w->want == next) {
+		/* Make sure we read lock before want */
+		if (ACCESS_ONCE(w->lock) == lock &&
+		    ACCESS_ONCE(w->want) == next) {
 			add_stats(RELEASED_SLOW_KICKED, 1);
 			xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
 			break;

[PATCH V12 12/14] kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi

[Raghavendra K T]

kvm uapi: Add KICK_CPU and PV_UNHALT definition to uapi

From: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>

this is needed by both guest and host.

Originally-from: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/uapi/asm/kvm_para.h |    1 +
 include/uapi/linux/kvm_para.h        |    1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 06fdbd9..94dc8ca 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -23,6 +23,7 @@
 #define KVM_FEATURE_ASYNC_PF		4
 #define KVM_FEATURE_STEAL_TIME		5
 #define KVM_FEATURE_PV_EOI		6
+#define KVM_FEATURE_PV_UNHALT		7
 
 /* The last 8 bits are used to indicate how to interpret the flags field
  * in pvclock structure. If no bits are set, all flags are ignored.
diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
index cea2c5c..2841f86 100644
--- a/include/uapi/linux/kvm_para.h
+++ b/include/uapi/linux/kvm_para.h
@@ -19,6 +19,7 @@
 #define KVM_HC_MMU_OP			2
 #define KVM_HC_FEATURES			3
 #define KVM_HC_PPC_MAP_MAGIC_PAGE	4
+#define KVM_HC_KICK_CPU			5
 
 /*
  * hypercalls use architecture specific

[PATCH V12 13/14] kvm guest : Add configuration support to enable debug information for KVM Guests

[Raghavendra K T]

kvm guest : Add configuration support to enable debug information for KVM Guests

From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Suzuki Poulose <suzuki@in.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/Kconfig |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 724ce55..f108f00 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -688,6 +688,15 @@ config KVM_GUEST
 	  underlying device model, the host provides the guest with
 	  timing infrastructure such as time of day, and system time
 
+config KVM_DEBUG_FS
+	bool "Enable debug information for KVM Guests in debugfs"
+	depends on KVM_GUEST && DEBUG_FS
+	default n
+	---help---
+	  This option enables collection of various statistics for KVM guest.
+	  Statistics are displayed in debugfs filesystem. Enabling this option
+	  may incur significant overhead.
+
 source "arch/x86/lguest/Kconfig"
 
 config PARAVIRT_TIME_ACCOUNTING

[PATCH V12 14/14] kvm : Paravirtual ticketlocks support for linux guests running on KVM hypervisor

[Raghavendra K T]

kvm : Paravirtual ticketlocks support for linux guests running on KVM hypervisor

From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>

During smp_boot_cpus  paravirtualied KVM guest detects if the hypervisor has
required feature (KVM_FEATURE_PV_UNHALT) to support pv-ticketlocks. If so,
 support for pv-ticketlocks is registered via pv_lock_ops.

Use KVM_HC_KICK_CPU hypercall to wakeup waiting/halted vcpu.

Signed-off-by: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Signed-off-by: Suzuki Poulose <suzuki@in.ibm.com>
[Raghu: check_zero race fix, enum for kvm_contention_stat, jumplabel related changes,
addition of safe_halt for irq enabled case, bailout spinning in nmi case(Gleb)]
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Acked-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/kvm_para.h |   14 ++
 arch/x86/kernel/kvm.c           |  262 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 274 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 695399f..427afcb 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -118,10 +118,20 @@ void kvm_async_pf_task_wait(u32 token);
 void kvm_async_pf_task_wake(u32 token);
 u32 kvm_read_and_reset_pf_reason(void);
 extern void kvm_disable_steal_time(void);
-#else
-#define kvm_guest_init() do { } while (0)
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+void __init kvm_spinlock_init(void);
+#else /* !CONFIG_PARAVIRT_SPINLOCKS */
+static inline void kvm_spinlock_init(void)
+{
+}
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
+
+#else /* CONFIG_KVM_GUEST */
+#define kvm_guest_init() do {} while (0)
 #define kvm_async_pf_task_wait(T) do {} while(0)
 #define kvm_async_pf_task_wake(T) do {} while(0)
+
 static inline u32 kvm_read_and_reset_pf_reason(void)
 {
 	return 0;
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index a96d32c..9b33a27 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -34,6 +34,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/kprobes.h>
+#include <linux/debugfs.h>
 #include <asm/timer.h>
 #include <asm/cpu.h>
 #include <asm/traps.h>
@@ -419,6 +420,7 @@ static void __init kvm_smp_prepare_boot_cpu(void)
 	WARN_ON(kvm_register_clock("primary cpu clock"));
 	kvm_guest_cpu_init();
 	native_smp_prepare_boot_cpu();
+	kvm_spinlock_init();
 }
 
 static void kvm_guest_cpu_online(void *dummy)
@@ -523,3 +525,263 @@ static __init int activate_jump_labels(void)
 	return 0;
 }
 arch_initcall(activate_jump_labels);
+
+/* Kick a cpu by its apicid. Used to wake up a halted vcpu */
+void kvm_kick_cpu(int cpu)
+{
+	int apicid;
+	unsigned long flags = 0;
+
+	apicid = per_cpu(x86_cpu_to_apicid, cpu);
+	kvm_hypercall2(KVM_HC_KICK_CPU, flags, apicid);
+}
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+
+enum kvm_contention_stat {
+	TAKEN_SLOW,
+	TAKEN_SLOW_PICKUP,
+	RELEASED_SLOW,
+	RELEASED_SLOW_KICKED,
+	NR_CONTENTION_STATS
+};
+
+#ifdef CONFIG_KVM_DEBUG_FS
+#define HISTO_BUCKETS	30
+
+static struct kvm_spinlock_stats
+{
+	u32 contention_stats[NR_CONTENTION_STATS];
+	u32 histo_spin_blocked[HISTO_BUCKETS+1];
+	u64 time_blocked;
+} spinlock_stats;
+
+static u8 zero_stats;
+
+static inline void check_zero(void)
+{
+	u8 ret;
+	u8 old;
+
+	old = ACCESS_ONCE(zero_stats);
+	if (unlikely(old)) {
+		ret = cmpxchg(&zero_stats, old, 0);
+		/* This ensures only one fellow resets the stat */
+		if (ret == old)
+			memset(&spinlock_stats, 0, sizeof(spinlock_stats));
+	}
+}
+
+static inline void add_stats(enum kvm_contention_stat var, u32 val)
+{
+	check_zero();
+	spinlock_stats.contention_stats[var] += val;
+}
+
+
+static inline u64 spin_time_start(void)
+{
+	return sched_clock();
+}
+
+static void __spin_time_accum(u64 delta, u32 *array)
+{
+	unsigned index;
+
+	index = ilog2(delta);
+	check_zero();
+
+	if (index < HISTO_BUCKETS)
+		array[index]++;
+	else
+		array[HISTO_BUCKETS]++;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+	u32 delta;
+
+	delta = sched_clock() - start;
+	__spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
+	spinlock_stats.time_blocked += delta;
+}
+
+static struct dentry *d_spin_debug;
+static struct dentry *d_kvm_debug;
+
+struct dentry *kvm_init_debugfs(void)
+{
+	d_kvm_debug = debugfs_create_dir("kvm", NULL);
+	if (!d_kvm_debug)
+		printk(KERN_WARNING "Could not create 'kvm' debugfs directory\n");
+
+	return d_kvm_debug;
+}
+
+static int __init kvm_spinlock_debugfs(void)
+{
+	struct dentry *d_kvm;
+
+	d_kvm = kvm_init_debugfs();
+	if (d_kvm == NULL)
+		return -ENOMEM;
+
+	d_spin_debug = debugfs_create_dir("spinlocks", d_kvm);
+
+	debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
+
+	debugfs_create_u32("taken_slow", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[TAKEN_SLOW]);
+	debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
+
+	debugfs_create_u32("released_slow", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[RELEASED_SLOW]);
+	debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
+		   &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
+
+	debugfs_create_u64("time_blocked", 0444, d_spin_debug,
+			   &spinlock_stats.time_blocked);
+
+	debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
+		     spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
+
+	return 0;
+}
+fs_initcall(kvm_spinlock_debugfs);
+#else  /* !CONFIG_KVM_DEBUG_FS */
+static inline void add_stats(enum kvm_contention_stat var, u32 val)
+{
+}
+
+static inline u64 spin_time_start(void)
+{
+	return 0;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+}
+#endif  /* CONFIG_KVM_DEBUG_FS */
+
+struct kvm_lock_waiting {
+	struct arch_spinlock *lock;
+	__ticket_t want;
+};
+
+/* cpus 'waiting' on a spinlock to become available */
+static cpumask_t waiting_cpus;
+
+/* Track spinlock on which a cpu is waiting */
+static DEFINE_PER_CPU(struct kvm_lock_waiting, lock_waiting);
+
+static void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
+{
+	struct kvm_lock_waiting *w;
+	int cpu;
+	u64 start;
+	unsigned long flags;
+
+	if (in_nmi())
+		return;
+
+	w = &__get_cpu_var(lock_waiting);
+	cpu = smp_processor_id();
+	start = spin_time_start();
+
+	/*
+	 * Make sure an interrupt handler can't upset things in a
+	 * partially setup state.
+	 */
+	local_irq_save(flags);
+
+	/*
+	 * The ordering protocol on this is that the "lock" pointer
+	 * may only be set non-NULL if the "want" ticket is correct.
+	 * If we're updating "want", we must first clear "lock".
+	 */
+	w->lock = NULL;
+	smp_wmb();
+	w->want = want;
+	smp_wmb();
+	w->lock = lock;
+
+	add_stats(TAKEN_SLOW, 1);
+
+	/*
+	 * This uses set_bit, which is atomic but we should not rely on its
+	 * reordering gurantees. So barrier is needed after this call.
+	 */
+	cpumask_set_cpu(cpu, &waiting_cpus);
+
+	barrier();
+
+	/*
+	 * Mark entry to slowpath before doing the pickup test to make
+	 * sure we don't deadlock with an unlocker.
+	 */
+	__ticket_enter_slowpath(lock);
+
+	/*
+	 * check again make sure it didn't become free while
+	 * we weren't looking.
+	 */
+	if (ACCESS_ONCE(lock->tickets.head) == want) {
+		add_stats(TAKEN_SLOW_PICKUP, 1);
+		goto out;
+	}
+
+	/*
+	 * halt until it's our turn and kicked. Note that we do safe halt
+	 * for irq enabled case to avoid hang when lock info is overwritten
+	 * in irq spinlock slowpath and no spurious interrupt occur to save us.
+	 */
+	if (arch_irqs_disabled_flags(flags))
+		halt();
+	else
+		safe_halt();
+
+out:
+	cpumask_clear_cpu(cpu, &waiting_cpus);
+	w->lock = NULL;
+	local_irq_restore(flags);
+	spin_time_accum_blocked(start);
+}
+PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
+
+/* Kick vcpu waiting on @lock->head to reach value @ticket */
+static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
+{
+	int cpu;
+
+	add_stats(RELEASED_SLOW, 1);
+	for_each_cpu(cpu, &waiting_cpus) {
+		const struct kvm_lock_waiting *w = &per_cpu(lock_waiting, cpu);
+		if (ACCESS_ONCE(w->lock) == lock &&
+		    ACCESS_ONCE(w->want) == ticket) {
+			add_stats(RELEASED_SLOW_KICKED, 1);
+			kvm_kick_cpu(cpu);
+			break;
+		}
+	}
+}
+
+/*
+ * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
+ */
+void __init kvm_spinlock_init(void)
+{
+	if (!kvm_para_available())
+		return;
+	/* Does host kernel support KVM_FEATURE_PV_UNHALT? */
+	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
+		return;
+
+	printk(KERN_INFO "KVM setup paravirtual spinlock\n");
+
+	static_key_slow_inc(&paravirt_ticketlocks_enabled);
+
+	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
+	pv_lock_ops.unlock_kick = kvm_unlock_kick;
+}
+#endif	/* CONFIG_PARAVIRT_SPINLOCKS */

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[H. Peter Anvin]

On 08/06/2013 04:40 AM, Raghavendra K T wrote:
> This series replaces the existing paravirtualized spinlock mechanism
> with a paravirtualized ticketlock mechanism. The series provides
> implementation for both Xen and KVM.
> 
> The current set of patches are for Xen/x86 spinlock/KVM guest side, to be included
> against -tip.
> 

What is the baseline for this patchset?  I tried to apply it on top of
3.11-rc4 and I got nontrivial conflicts.

	-hpa

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/07/2013 02:31 AM, H. Peter Anvin wrote:
>
> What is the baseline for this patchset?  I tried to apply it on top of
> 3.11-rc4 and I got nontrivial conflicts.
>

I had based it on top of 445363e8 [ Merge branch 'perf/urgent']
of tip.  Sorry for not mentioning that.

Please let me know, if I should rebase again.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[H. Peter Anvin]

On 08/06/2013 07:54 PM, Raghavendra K T wrote:
> On 08/07/2013 02:31 AM, H. Peter Anvin wrote:
>>
>> What is the baseline for this patchset?  I tried to apply it on top of
>> 3.11-rc4 and I got nontrivial conflicts.
>>
> 
> I had based it on top of 445363e8 [ Merge branch 'perf/urgent']
> of tip.  Sorry for not mentioning that.
> 
> Please let me know, if I should rebase again.
> 

tip:master is not a stable branch; it is more like linux-next.  We need
to figure out which topic branches are dependencies for this set.

	-hpa

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/07/2013 10:18 AM, H. Peter Anvin wrote:
>> Please let me know, if I should rebase again.
>>
>
> tip:master is not a stable branch; it is more like linux-next.  We need
> to figure out which topic branches are dependencies for this set.

Okay. I 'll start looking at the branches that would get affected.
(Xen, kvm are obvious ones).
Please do let me know the branches I might have to check for.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Konrad Rzeszutek Wilk]

On Wed, Aug 07, 2013 at 12:15:21PM +0530, Raghavendra K T wrote:
> On 08/07/2013 10:18 AM, H. Peter Anvin wrote:
> >>Please let me know, if I should rebase again.
> >>
> >
> >tip:master is not a stable branch; it is more like linux-next.  We need
> >to figure out which topic branches are dependencies for this set.
> 
> Okay. I 'll start looking at the branches that would get affected.
> (Xen, kvm are obvious ones).
> Please do let me know the branches I might have to check for.

From the Xen standpoint anything past v3.11-rc4 would work.

> 
> 
> 
> 
> 

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Gleb Natapov]

On Wed, Aug 07, 2013 at 08:50:12PM -0400, Konrad Rzeszutek Wilk wrote:
> On Wed, Aug 07, 2013 at 12:15:21PM +0530, Raghavendra K T wrote:
> > On 08/07/2013 10:18 AM, H. Peter Anvin wrote:
> > >>Please let me know, if I should rebase again.
> > >>
> > >
> > >tip:master is not a stable branch; it is more like linux-next.  We need
> > >to figure out which topic branches are dependencies for this set.
> > 
> > Okay. I 'll start looking at the branches that would get affected.
> > (Xen, kvm are obvious ones).
> > Please do let me know the branches I might have to check for.
> 
> >From the Xen standpoint anything past v3.11-rc4 would work.
> 
For KVM as early as past v3.11-rc1 would be OK.

--
			Gleb.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[H. Peter Anvin]

On 08/07/2013 06:02 PM, Gleb Natapov wrote:
> On Wed, Aug 07, 2013 at 08:50:12PM -0400, Konrad Rzeszutek Wilk wrote:
>> On Wed, Aug 07, 2013 at 12:15:21PM +0530, Raghavendra K T wrote:
>>> On 08/07/2013 10:18 AM, H. Peter Anvin wrote:
>>>>> Please let me know, if I should rebase again.
>>>>>
>>>>
>>>> tip:master is not a stable branch; it is more like linux-next.  We need
>>>> to figure out which topic branches are dependencies for this set.
>>>
>>> Okay. I 'll start looking at the branches that would get affected.
>>> (Xen, kvm are obvious ones).
>>> Please do let me know the branches I might have to check for.
>>
>> >From the Xen standpoint anything past v3.11-rc4 would work.
>>
> For KVM as early as past v3.11-rc1 would be OK.
> 

I'm still completely confused as to the base of this patchset.  The
first patch has the following hunk for arch/x86/include/asm/paravirt.h:


--- arch/x86/include/asm/paravirt.h
+++ arch/x86/include/asm/paravirt.h
@@ -718,7 +718,7 @@
        PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
 }

-static __always_inline void ____ticket_unlock_kick(struct arch_spinlock
*lock,
+static __always_inline void __ticket_unlock_kick(struct arch_spinlock
*lock,
                                                        __ticket_t ticket)
 {
        PVOP_VCALL2(pv_lock_ops.unlock_kick, lock, ticket);


However, there is no ticket_unlock_kick in paravirt.h in either
tip:master nor in linus...

	-hpa

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[H. Peter Anvin]

On 08/08/2013 02:13 PM, H. Peter Anvin wrote:
> On 08/07/2013 06:02 PM, Gleb Natapov wrote:
>> On Wed, Aug 07, 2013 at 08:50:12PM -0400, Konrad Rzeszutek Wilk wrote:
>>> On Wed, Aug 07, 2013 at 12:15:21PM +0530, Raghavendra K T wrote:
>>>> On 08/07/2013 10:18 AM, H. Peter Anvin wrote:
>>>>>> Please let me know, if I should rebase again.
>>>>>>
>>>>>
>>>>> tip:master is not a stable branch; it is more like linux-next.  We need
>>>>> to figure out which topic branches are dependencies for this set.
>>>>
>>>> Okay. I 'll start looking at the branches that would get affected.
>>>> (Xen, kvm are obvious ones).
>>>> Please do let me know the branches I might have to check for.
>>>
>>> >From the Xen standpoint anything past v3.11-rc4 would work.
>>>
>> For KVM as early as past v3.11-rc1 would be OK.
>>
> 
> I'm still completely confused as to the base of this patchset.  The
> first patch has the following hunk for arch/x86/include/asm/paravirt.h:
> 

Okay, I figured it out.

One of several problems with the formatting of this patchset is that it
has one- and two-digit patch numbers in the headers, which meant that my
scripts tried to apply patch 10 first.

	-hpa

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/09/2013 04:34 AM, H. Peter Anvin wrote:
>
> Okay, I figured it out.
>
> One of several problems with the formatting of this patchset is that it
> has one- and two-digit patch numbers in the headers, which meant that my
> scripts tried to apply patch 10 first.
>

My bad. I 'll send out in uniform digit form next time.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Konrad Rzeszutek Wilk]

On Fri, Aug 09, 2013 at 06:20:02PM +0530, Raghavendra K T wrote:
> On 08/09/2013 04:34 AM, H. Peter Anvin wrote:
> >
> >Okay, I figured it out.
> >
> >One of several problems with the formatting of this patchset is that it
> >has one- and two-digit patch numbers in the headers, which meant that my
> >scripts tried to apply patch 10 first.
> >
> 
> My bad. I 'll send out in uniform digit form next time.
> 

If you use 'git format-patch --subject-prefix "PATCH V14" v3.11-rc4..'
and 'git send-email --subject "[PATCH V14] bla blah" ..'
that should be automatically taken care of?

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/09/2013 06:30 PM, Konrad Rzeszutek Wilk wrote:
>> My bad. I 'll send out in uniform digit form next time.
>>
>
> If you use 'git format-patch --subject-prefix "PATCH V14" v3.11-rc4..'
> and 'git send-email --subject "[PATCH V14] bla blah" ..'
> that should be automatically taken care of?
>

Thanks Konrad.
Yes. it should. I am planning to use git send-email instead of custom
script.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[H. Peter Anvin]

On 08/09/2013 06:00 AM, Konrad Rzeszutek Wilk wrote:
> On Fri, Aug 09, 2013 at 06:20:02PM +0530, Raghavendra K T wrote:
>> On 08/09/2013 04:34 AM, H. Peter Anvin wrote:
>>>
>>> Okay, I figured it out.
>>>
>>> One of several problems with the formatting of this patchset is that it
>>> has one- and two-digit patch numbers in the headers, which meant that my
>>> scripts tried to apply patch 10 first.
>>>
>>
>> My bad. I 'll send out in uniform digit form next time.
>>
> 
> If you use 'git format-patch --subject-prefix "PATCH V14" v3.11-rc4..'
> and 'git send-email --subject "[PATCH V14] bla blah" ..'
> that should be automatically taken care of?
> 

Indeed it should.

Another problem with this patchset was that the subject was duplicated
in the body, which meant the tools didn't pick up the From: line.  I
ended up having to manually edit them.

That seems to have been fixed, too, in V13.

	-hpa

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/07/2013 12:15 PM, Raghavendra K T wrote:
> On 08/07/2013 10:18 AM, H. Peter Anvin wrote:
>> tip:master is not a stable branch; it is more like linux-next.  We need
>> to figure out which topic branches are dependencies for this set.
>
> Okay. I 'll start looking at the branches that would get affected.
> (Xen, kvm are obvious ones).
> Please do let me know the branches I might have to check for.

On Linus tree,
I am seeing patch getting applied to arch/x86/Kconfig at some offset

Hunk #1 succeeded at 632 (offset -31 lines).
Hunk #2 succeeded at 657 (offset -31 lines).

since patches are based on -rc4, Xen, kvm should not have problem
as pointed by Gleb, Konrad.
I did not see change in tip's jumplabel/core-spinlock tree that would
affect it.

Peter, could you please point me to the conflict, so that I can help
there which saves time and trouble to maintainers.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[H. Peter Anvin]

The kbuild test bot is reporting some pretty serious errors for this
patchset.  I think these are serious enough that the patchset will need
to be respun.

	-hpa

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/09/2013 06:34 AM, H. Peter Anvin wrote:
> The kbuild test bot is reporting some pretty serious errors for this
> patchset.  I think these are serious enough that the patchset will need
> to be respun.
>

I  am working on that.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/09/2013 06:34 AM, H. Peter Anvin wrote:
> The kbuild test bot is reporting some pretty serious errors for this
> patchset.  I think these are serious enough that the patchset will need
> to be respun.
>

There were two problems:
(1) we were including spinlock_types.h in 
arch/x86/include/asm/paravirt_types.h.

This was resulting in redefinition of arch_spinlock_t for non SMP kernel

solution was :
conditional inclusion of spinlock_types.h like below

#ifdef CONFIG_SMP
#include <asm/spinlock_types.h>
#else
typedef u16 __ticket_t;
#endif

(we needed __ticket_t declaration for UP)

(2) we had forward declaration of atomic_read in jumpl_label.
It was causing problem for alpha, which has macro for atomic_read
instead of static inline.

Solution was to remove forward declaration and have atomic.h included.

Peter,
  the above two changes needs small changes in patch 1 and patch 9.
I 'll be resending only those two patches.

I am happy to resend the whole series if it is better and easier for
you.

Re: [PATCH V12 0/14] Paravirtualized ticket spinlocks

[Raghavendra K T]

On 08/09/2013 06:34 AM, H. Peter Anvin wrote:
> The kbuild test bot is reporting some pretty serious errors for this
> patchset.  I think these are serious enough that the patchset will need
> to be respun.
>

Sent V13, there were 3 patches in total that changed due to dependency.