lkml.org 
[lkml]   [2008]   [Mar]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 5/6] Add down_timeout and change ACPI to use it
Date
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>
---
drivers/acpi/osl.c | 89 +++++++++++----------------------------------
include/linux/semaphore.h | 6 +++
kernel/semaphore.c | 42 ++++++++++++++++++----
3 files changed, 62 insertions(+), 75 deletions(-)

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 065819b..2adfb6d 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -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");
@@ -848,7 +853,6 @@ 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;
@@ -875,12 +879,12 @@ 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;

@@ -888,21 +892,15 @@ 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;

@@ -912,58 +910,14 @@ 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,
@@ -986,7 +940,6 @@ 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;

diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h
index 88f2a28..a107aeb 100644
--- a/include/linux/semaphore.h
+++ b/include/linux/semaphore.h
@@ -75,6 +75,12 @@ 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().
*/
diff --git a/kernel/semaphore.c b/kernel/semaphore.c
index 2da2aed..5a12a85 100644
--- a/kernel/semaphore.c
+++ b/kernel/semaphore.c
@@ -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)
--
1.5.4.3


\
 
 \ /
  Last update: 2008-03-14 22:23    [W:0.048 / U:8.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site