From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001 From: André Fabian Silva Delgado Date: Wed, 5 Aug 2015 17:04:01 -0300 Subject: Initial import --- arch/tile/lib/spinlock_32.c | 259 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 259 insertions(+) create mode 100644 arch/tile/lib/spinlock_32.c (limited to 'arch/tile/lib/spinlock_32.c') diff --git a/arch/tile/lib/spinlock_32.c b/arch/tile/lib/spinlock_32.c new file mode 100644 index 000000000..b34f79aad --- /dev/null +++ b/arch/tile/lib/spinlock_32.c @@ -0,0 +1,259 @@ +/* + * Copyright 2010 Tilera Corporation. All Rights Reserved. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation, version 2. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or + * NON INFRINGEMENT. See the GNU General Public License for + * more details. + */ + +#include +#include +#include +#include + +#include "spinlock_common.h" + +void arch_spin_lock(arch_spinlock_t *lock) +{ + int my_ticket; + int iterations = 0; + int delta; + + while ((my_ticket = __insn_tns((void *)&lock->next_ticket)) & 1) + delay_backoff(iterations++); + + /* Increment the next ticket number, implicitly releasing tns lock. */ + lock->next_ticket = my_ticket + TICKET_QUANTUM; + + /* Wait until it's our turn. */ + while ((delta = my_ticket - lock->current_ticket) != 0) + relax((128 / CYCLES_PER_RELAX_LOOP) * delta); +} +EXPORT_SYMBOL(arch_spin_lock); + +int arch_spin_trylock(arch_spinlock_t *lock) +{ + /* + * Grab a ticket; no need to retry if it's busy, we'll just + * treat that the same as "locked", since someone else + * will lock it momentarily anyway. + */ + int my_ticket = __insn_tns((void *)&lock->next_ticket); + + if (my_ticket == lock->current_ticket) { + /* Not currently locked, so lock it by keeping this ticket. */ + lock->next_ticket = my_ticket + TICKET_QUANTUM; + /* Success! */ + return 1; + } + + if (!(my_ticket & 1)) { + /* Release next_ticket. */ + lock->next_ticket = my_ticket; + } + + return 0; +} +EXPORT_SYMBOL(arch_spin_trylock); + +void arch_spin_unlock_wait(arch_spinlock_t *lock) +{ + u32 iterations = 0; + while (arch_spin_is_locked(lock)) + delay_backoff(iterations++); +} +EXPORT_SYMBOL(arch_spin_unlock_wait); + +/* + * The low byte is always reserved to be the marker for a "tns" operation + * since the low bit is set to "1" by a tns. The next seven bits are + * zeroes. The next byte holds the "next" writer value, i.e. the ticket + * available for the next task that wants to write. The third byte holds + * the current writer value, i.e. the writer who holds the current ticket. + * If current == next == 0, there are no interested writers. + */ +#define WR_NEXT_SHIFT _WR_NEXT_SHIFT +#define WR_CURR_SHIFT _WR_CURR_SHIFT +#define WR_WIDTH _WR_WIDTH +#define WR_MASK ((1 << WR_WIDTH) - 1) + +/* + * The last eight bits hold the active reader count. This has to be + * zero before a writer can start to write. + */ +#define RD_COUNT_SHIFT _RD_COUNT_SHIFT +#define RD_COUNT_WIDTH _RD_COUNT_WIDTH +#define RD_COUNT_MASK ((1 << RD_COUNT_WIDTH) - 1) + + +/* + * We can get the read lock if everything but the reader bits (which + * are in the high part of the word) is zero, i.e. no active or + * waiting writers, no tns. + * + * We guard the tns/store-back with an interrupt critical section to + * preserve the semantic that the same read lock can be acquired in an + * interrupt context. + */ +int arch_read_trylock(arch_rwlock_t *rwlock) +{ + u32 val; + __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1); + val = __insn_tns((int *)&rwlock->lock); + if (likely((val << _RD_COUNT_WIDTH) == 0)) { + val += 1 << RD_COUNT_SHIFT; + rwlock->lock = val; + __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0); + BUG_ON(val == 0); /* we don't expect wraparound */ + return 1; + } + if ((val & 1) == 0) + rwlock->lock = val; + __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0); + return 0; +} +EXPORT_SYMBOL(arch_read_trylock); + +/* + * Spin doing arch_read_trylock() until we acquire the lock. + * ISSUE: This approach can permanently starve readers. A reader who sees + * a writer could instead take a ticket lock (just like a writer would), + * and atomically enter read mode (with 1 reader) when it gets the ticket. + * This way both readers and writers would always make forward progress + * in a finite time. + */ +void arch_read_lock(arch_rwlock_t *rwlock) +{ + u32 iterations = 0; + while (unlikely(!arch_read_trylock(rwlock))) + delay_backoff(iterations++); +} +EXPORT_SYMBOL(arch_read_lock); + +void arch_read_unlock(arch_rwlock_t *rwlock) +{ + u32 val, iterations = 0; + + mb(); /* guarantee anything modified under the lock is visible */ + for (;;) { + __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 1); + val = __insn_tns((int *)&rwlock->lock); + if (likely((val & 1) == 0)) { + rwlock->lock = val - (1 << _RD_COUNT_SHIFT); + __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0); + break; + } + __insn_mtspr(SPR_INTERRUPT_CRITICAL_SECTION, 0); + delay_backoff(iterations++); + } +} +EXPORT_SYMBOL(arch_read_unlock); + +/* + * We don't need an interrupt critical section here (unlike for + * arch_read_lock) since we should never use a bare write lock where + * it could be interrupted by code that could try to re-acquire it. + */ +void arch_write_lock(arch_rwlock_t *rwlock) +{ + /* + * The trailing underscore on this variable (and curr_ below) + * reminds us that the high bits are garbage; we mask them out + * when we compare them. + */ + u32 my_ticket_; + u32 iterations = 0; + u32 val = __insn_tns((int *)&rwlock->lock); + + if (likely(val == 0)) { + rwlock->lock = 1 << _WR_NEXT_SHIFT; + return; + } + + /* + * Wait until there are no readers, then bump up the next + * field and capture the ticket value. + */ + for (;;) { + if (!(val & 1)) { + if ((val >> RD_COUNT_SHIFT) == 0) + break; + rwlock->lock = val; + } + delay_backoff(iterations++); + val = __insn_tns((int *)&rwlock->lock); + } + + /* Take out the next ticket and extract my ticket value. */ + rwlock->lock = __insn_addb(val, 1 << WR_NEXT_SHIFT); + my_ticket_ = val >> WR_NEXT_SHIFT; + + /* Wait until the "current" field matches our ticket. */ + for (;;) { + u32 curr_ = val >> WR_CURR_SHIFT; + u32 delta = ((my_ticket_ - curr_) & WR_MASK); + if (likely(delta == 0)) + break; + + /* Delay based on how many lock-holders are still out there. */ + relax((256 / CYCLES_PER_RELAX_LOOP) * delta); + + /* + * Get a non-tns value to check; we don't need to tns + * it ourselves. Since we're not tns'ing, we retry + * more rapidly to get a valid value. + */ + while ((val = rwlock->lock) & 1) + relax(4); + } +} +EXPORT_SYMBOL(arch_write_lock); + +int arch_write_trylock(arch_rwlock_t *rwlock) +{ + u32 val = __insn_tns((int *)&rwlock->lock); + + /* + * If a tns is in progress, or there's a waiting or active locker, + * or active readers, we can't take the lock, so give up. + */ + if (unlikely(val != 0)) { + if (!(val & 1)) + rwlock->lock = val; + return 0; + } + + /* Set the "next" field to mark it locked. */ + rwlock->lock = 1 << _WR_NEXT_SHIFT; + return 1; +} +EXPORT_SYMBOL(arch_write_trylock); + +void arch_write_unlock(arch_rwlock_t *rwlock) +{ + u32 val, eq, mask; + + mb(); /* guarantee anything modified under the lock is visible */ + val = __insn_tns((int *)&rwlock->lock); + if (likely(val == (1 << _WR_NEXT_SHIFT))) { + rwlock->lock = 0; + return; + } + while (unlikely(val & 1)) { + /* Limited backoff since we are the highest-priority task. */ + relax(4); + val = __insn_tns((int *)&rwlock->lock); + } + mask = 1 << WR_CURR_SHIFT; + val = __insn_addb(val, mask); + eq = __insn_seqb(val, val << (WR_CURR_SHIFT - WR_NEXT_SHIFT)); + val = __insn_mz(eq & mask, val); + rwlock->lock = val; +} +EXPORT_SYMBOL(arch_write_unlock); -- cgit v1.2.3-54-g00ecf