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Add down_timeout and change ACPI to use it 

ACPI currently emulates a timeout for semaphores with calls to
down_trylock and sleep.  This produces horrible behaviour in terms of
fairness and excessive wakeups.  Now that we have a unified semaphore
implementation, adding a real down_trylock is almost trivial.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
This commit is contained in:
Matthew Wilcox 2008-03-14 13:43:13 -04:00 committed by Matthew Wilcox
parent f06d968658
commit f1241c87a1
3 changed files with 62 additions and 75 deletions
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89
drivers/acpi/osl.c
View File

@ -4,6 +4,8 @@
* Copyright (C) 2000 Andrew Henroid
* Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com>
* Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com>
* Copyright (c) 2008 Intel Corporation
* Author: Matthew Wilcox <willy@linux.intel.com>
*
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
@ -37,15 +39,18 @@
#include <linux/workqueue.h>
#include <linux/nmi.h>
#include <linux/acpi.h>
#include <acpi/acpi.h>
#include <asm/io.h>
#include <acpi/acpi_bus.h>
#include <acpi/processor.h>
#include <asm/uaccess.h>
#include <linux/efi.h>
#include <linux/ioport.h>
#include <linux/list.h>
#include <linux/jiffies.h>
#include <linux/semaphore.h>
#include <asm/io.h>
#include <asm/uaccess.h>
#include <acpi/acpi.h>
#include <acpi/acpi_bus.h>
#include <acpi/processor.h>
#define _COMPONENT ACPI_OS_SERVICES
ACPI_MODULE_NAME("osl");
@ -764,7 +769,6 @@ acpi_os_create_semaphore(u32 max_units, u32 initial_units, acpi_handle * handle)
{
struct semaphore *sem = NULL;
sem = acpi_os_allocate(sizeof(struct semaphore));
if (!sem)
return AE_NO_MEMORY;
@ -791,12 +795,12 @@ acpi_status acpi_os_delete_semaphore(acpi_handle handle)
{
struct semaphore *sem = (struct semaphore *)handle;
if (!sem)
return AE_BAD_PARAMETER;
ACPI_DEBUG_PRINT((ACPI_DB_MUTEX, "Deleting semaphore[%p].\n", handle));
BUG_ON(!list_empty(&sem->wait_list));
kfree(sem);
sem = NULL;
@ -804,21 +808,15 @@ acpi_status acpi_os_delete_semaphore(acpi_handle handle)
}
/*
* TODO: The kernel doesn't have a 'down_timeout' function -- had to
* improvise. The process is to sleep for one scheduler quantum
* until the semaphore becomes available. Downside is that this
* may result in starvation for timeout-based waits when there's
* lots of semaphore activity.
*
* TODO: Support for units > 1?
*/
acpi_status acpi_os_wait_semaphore(acpi_handle handle, u32 units, u16 timeout)
{
acpi_status status = AE_OK;
struct semaphore *sem = (struct semaphore *)handle;
long jiffies;
int ret = 0;
if (!sem || (units < 1))
return AE_BAD_PARAMETER;
@ -828,58 +826,14 @@ acpi_status acpi_os_wait_semaphore(acpi_handle handle, u32 units, u16 timeout)
ACPI_DEBUG_PRINT((ACPI_DB_MUTEX, "Waiting for semaphore[%p|%d|%d]\n",
handle, units, timeout));
/*
* This can be called during resume with interrupts off.
* Like boot-time, we should be single threaded and will
* always get the lock if we try -- timeout or not.
* If this doesn't succeed, then we will oops courtesy of
* might_sleep() in down().
*/
if (!down_trylock(sem))
return AE_OK;
switch (timeout) {
/*
* No Wait:
* --------
* A zero timeout value indicates that we shouldn't wait - just
* acquire the semaphore if available otherwise return AE_TIME
* (a.k.a. 'would block').
*/
case 0:
if (down_trylock(sem))
status = AE_TIME;
break;
/*
* Wait Indefinitely:
* ------------------
*/
case ACPI_WAIT_FOREVER:
down(sem);
break;
/*
* Wait w/ Timeout:
* ----------------
*/
default:
// TODO: A better timeout algorithm?
{
int i = 0;
static const int quantum_ms = 1000 / HZ;
ret = down_trylock(sem);
for (i = timeout; (i > 0 && ret != 0); i -= quantum_ms) {
schedule_timeout_interruptible(1);
ret = down_trylock(sem);
}
if (ret != 0)
status = AE_TIME;
}
break;
}
if (timeout == ACPI_WAIT_FOREVER)
jiffies = MAX_SCHEDULE_TIMEOUT;
else
jiffies = msecs_to_jiffies(timeout);
ret = down_timeout(sem, jiffies);
if (ret)
status = AE_TIME;
if (ACPI_FAILURE(status)) {
ACPI_DEBUG_PRINT((ACPI_DB_MUTEX,
@ -902,7 +856,6 @@ acpi_status acpi_os_signal_semaphore(acpi_handle handle, u32 units)
{
struct semaphore *sem = (struct semaphore *)handle;
if (!sem || (units < 1))
return AE_BAD_PARAMETER;

6
include/linux/semaphore.h
View File

@ -74,6 +74,12 @@ extern int __must_check down_killable(struct semaphore *sem);
*/
extern int __must_check down_trylock(struct semaphore *sem);
/*
* As down(), except this function will return -ETIME if it fails to
* acquire the semaphore within the specified number of jiffies.
*/
extern int __must_check down_timeout(struct semaphore *sem, long jiffies);
/*
* Release the semaphore. Unlike mutexes, up() may be called from any
* context and even by tasks which have never called down().

42
kernel/semaphore.c
View File

@ -35,6 +35,7 @@
static noinline void __down(struct semaphore *sem);
static noinline int __down_interruptible(struct semaphore *sem);
static noinline int __down_killable(struct semaphore *sem);
static noinline int __down_timeout(struct semaphore *sem, long jiffies);
static noinline void __up(struct semaphore *sem);
void down(struct semaphore *sem)
@ -104,6 +105,20 @@ int down_trylock(struct semaphore *sem)
}
EXPORT_SYMBOL(down_trylock);
int down_timeout(struct semaphore *sem, long jiffies)
{
unsigned long flags;
int result = 0;
spin_lock_irqsave(&sem->lock, flags);
if (unlikely(sem->count-- <= 0))
result = __down_timeout(sem, jiffies);
spin_unlock_irqrestore(&sem->lock, flags);
return result;
}
EXPORT_SYMBOL(down_timeout);
void up(struct semaphore *sem)
{
unsigned long flags;
@ -142,10 +157,12 @@ static noinline void __sched __up_down_common(struct semaphore *sem)
}
/*
* Because this function is inlined, the 'state' parameter will be constant,
* and thus optimised away by the compiler.
* Because this function is inlined, the 'state' parameter will be
* constant, and thus optimised away by the compiler. Likewise the
* 'timeout' parameter for the cases without timeouts.
*/
static inline int __sched __down_common(struct semaphore *sem, long state)
static inline int __sched __down_common(struct semaphore *sem, long state,
long timeout)
{
int result = 0;
struct task_struct *task = current;
@ -160,14 +177,20 @@ static inline int __sched __down_common(struct semaphore *sem, long state)
goto interrupted;
if (state == TASK_KILLABLE && fatal_signal_pending(task))
goto interrupted;
if (timeout <= 0)
goto timed_out;
__set_task_state(task, state);
spin_unlock_irq(&sem->lock);
schedule();
timeout = schedule_timeout(timeout);
spin_lock_irq(&sem->lock);
if (waiter.up)
goto woken;
}
timed_out:
list_del(&waiter.list);
result = -ETIME;
goto woken;
interrupted:
list_del(&waiter.list);
result = -EINTR;
@ -187,17 +210,22 @@ static inline int __sched __down_common(struct semaphore *sem, long state)
static noinline void __sched __down(struct semaphore *sem)
{
__down_common(sem, TASK_UNINTERRUPTIBLE);
__down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
}
static noinline int __sched __down_interruptible(struct semaphore *sem)
{
return __down_common(sem, TASK_INTERRUPTIBLE);
return __down_common(sem, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
}
static noinline int __sched __down_killable(struct semaphore *sem)
{
return __down_common(sem, TASK_KILLABLE);
return __down_common(sem, TASK_KILLABLE, MAX_SCHEDULE_TIMEOUT);
}
static noinline int __sched __down_timeout(struct semaphore *sem, long jiffies)
{
return __down_common(sem, TASK_UNINTERRUPTIBLE, jiffies);
}
static noinline void __sched __up(struct semaphore *sem)