diff options
| -rw-r--r-- | arch/powerpc/lib/qspinlock.c | 99 |
1 files changed, 87 insertions, 12 deletions
diff --git a/arch/powerpc/lib/qspinlock.c b/arch/powerpc/lib/qspinlock.c index 4d74db0e565f..18e21574e6c5 100644 --- a/arch/powerpc/lib/qspinlock.c +++ b/arch/powerpc/lib/qspinlock.c @@ -5,6 +5,7 @@ #include <linux/percpu.h> #include <linux/smp.h> #include <asm/qspinlock.h> +#include <asm/paravirt.h> #define MAX_NODES 4 @@ -24,14 +25,16 @@ static int steal_spins __read_mostly = (1 << 5); static bool maybe_stealers __read_mostly = true; static int head_spins __read_mostly = (1 << 8); +static bool pv_yield_owner __read_mostly = true; + static DEFINE_PER_CPU_ALIGNED(struct qnodes, qnodes); -static __always_inline int get_steal_spins(void) +static __always_inline int get_steal_spins(bool paravirt) { return steal_spins; } -static __always_inline int get_head_spins(void) +static __always_inline int get_head_spins(bool paravirt) { return head_spins; } @@ -46,6 +49,11 @@ static inline int decode_tail_cpu(u32 val) return (val >> _Q_TAIL_CPU_OFFSET) - 1; } +static inline int get_owner_cpu(u32 val) +{ + return (val & _Q_OWNER_CPU_MASK) >> _Q_OWNER_CPU_OFFSET; +} + /* * Try to acquire the lock if it was not already locked. If the tail matches * mytail then clear it, otherwise leave it unchnaged. Return previous value. @@ -150,7 +158,45 @@ static struct qnode *get_tail_qnode(struct qspinlock *lock, u32 val) BUG(); } -static inline bool try_to_steal_lock(struct qspinlock *lock) +static __always_inline void yield_to_locked_owner(struct qspinlock *lock, u32 val, bool paravirt) +{ + int owner; + u32 yield_count; + + BUG_ON(!(val & _Q_LOCKED_VAL)); + + if (!paravirt) + goto relax; + + if (!pv_yield_owner) + goto relax; + + owner = get_owner_cpu(val); + yield_count = yield_count_of(owner); + + if ((yield_count & 1) == 0) + goto relax; /* owner vcpu is running */ + + /* + * Read the lock word after sampling the yield count. On the other side + * there may a wmb because the yield count update is done by the + * hypervisor preemption and the value update by the OS, however this + * ordering might reduce the chance of out of order accesses and + * improve the heuristic. + */ + smp_rmb(); + + if (READ_ONCE(lock->val) == val) { + yield_to_preempted(owner, yield_count); + /* Don't relax if we yielded. Maybe we should? */ + return; + } +relax: + cpu_relax(); +} + + +static __always_inline bool try_to_steal_lock(struct qspinlock *lock, bool paravirt) { int iters = 0; @@ -168,16 +214,16 @@ static inline bool try_to_steal_lock(struct qspinlock *lock) if (__queued_spin_trylock_steal(lock)) return true; } else { - cpu_relax(); + yield_to_locked_owner(lock, val, paravirt); } iters++; - } while (iters < get_steal_spins()); + } while (iters < get_steal_spins(paravirt)); return false; } -static inline void queued_spin_lock_mcs_queue(struct qspinlock *lock) +static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, bool paravirt) { struct qnodes *qnodesp; struct qnode *next, *node; @@ -235,12 +281,12 @@ again: if (!(val & _Q_LOCKED_VAL)) break; - cpu_relax(); + yield_to_locked_owner(lock, val, paravirt); if (!maybe_stealers) continue; iters++; - if (!mustq && iters >= get_head_spins()) { + if (!mustq && iters >= get_head_spins(paravirt)) { mustq = true; set_mustq(lock); val |= _Q_MUST_Q_VAL; @@ -276,10 +322,20 @@ release: void queued_spin_lock_slowpath(struct qspinlock *lock) { - if (try_to_steal_lock(lock)) - return; - - queued_spin_lock_mcs_queue(lock); + /* + * This looks funny, but it induces the compiler to inline both + * sides of the branch rather than share code as when the condition + * is passed as the paravirt argument to the functions. + */ + if (IS_ENABLED(CONFIG_PARAVIRT_SPINLOCKS) && is_shared_processor()) { + if (try_to_steal_lock(lock, true)) + return; + queued_spin_lock_mcs_queue(lock, true); + } else { + if (try_to_steal_lock(lock, false)) + return; + queued_spin_lock_mcs_queue(lock, false); + } } EXPORT_SYMBOL(queued_spin_lock_slowpath); @@ -345,10 +401,29 @@ static int head_spins_get(void *data, u64 *val) DEFINE_SIMPLE_ATTRIBUTE(fops_head_spins, head_spins_get, head_spins_set, "%llu\n"); +static int pv_yield_owner_set(void *data, u64 val) +{ + pv_yield_owner = !!val; + + return 0; +} + +static int pv_yield_owner_get(void *data, u64 *val) +{ + *val = pv_yield_owner; + + return 0; +} + +DEFINE_SIMPLE_ATTRIBUTE(fops_pv_yield_owner, pv_yield_owner_get, pv_yield_owner_set, "%llu\n"); + static __init int spinlock_debugfs_init(void) { debugfs_create_file("qspl_steal_spins", 0600, arch_debugfs_dir, NULL, &fops_steal_spins); debugfs_create_file("qspl_head_spins", 0600, arch_debugfs_dir, NULL, &fops_head_spins); + if (is_shared_processor()) { + debugfs_create_file("qspl_pv_yield_owner", 0600, arch_debugfs_dir, NULL, &fops_pv_yield_owner); + } return 0; } |