#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)
{
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;
}
#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)
{
}
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();
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
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);
projects / karo-tx-linux.git / commitdiff