Release 4.14 arch/tile/lib/spinlock_32.c
/*
* 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 <linux/spinlock.h>
#include <linux/module.h>
#include <asm/processor.h>
#include <arch/spr_def.h>
#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);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 81 | 100.00% | 1 | 100.00% |
| Total | 81 | 100.00% | 1 | 100.00% |
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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 69 | 100.00% | 1 | 100.00% |
| Total | 69 | 100.00% | 1 | 100.00% |
EXPORT_SYMBOL(arch_spin_trylock);
/*
* 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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 104 | 100.00% | 2 | 100.00% |
| Total | 104 | 100.00% | 2 | 100.00% |
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++);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 31 | 100.00% | 2 | 100.00% |
| Total | 31 | 100.00% | 2 | 100.00% |
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++);
}
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 93 | 96.88% | 2 | 66.67% |
| Roel Kluin | 3 | 3.12% | 1 | 33.33% |
| Total | 96 | 100.00% | 3 | 100.00% |
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);
}
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 197 | 100.00% | 3 | 100.00% |
| Total | 197 | 100.00% | 3 | 100.00% |
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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 66 | 100.00% | 2 | 100.00% |
| Total | 66 | 100.00% | 2 | 100.00% |
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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 134 | 100.00% | 2 | 100.00% |
| Total | 134 | 100.00% | 2 | 100.00% |
EXPORT_SYMBOL(arch_write_unlock);
Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Chris Metcalf | 864 | 99.65% | 3 | 75.00% |
| Roel Kluin | 3 | 0.35% | 1 | 25.00% |
| Total | 867 | 100.00% | 4 | 100.00% |
Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.