mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-23 12:43:55 +08:00
ce6711f3d1
Commit 5a505085f0
("mm/rmap: Convert the struct anon_vma::mutex
to an rwsem") changed struct anon_vma::mutex to an rwsem, which
caused aim7 fork_test performance to drop by 50%.
Yuanhan Liu did the following excellent analysis:
https://lkml.org/lkml/2013/1/29/84
and found that the regression is caused by strict, serialized,
FIFO sequential write-ownership of rwsems. Ingo suggested
implementing opportunistic lock-stealing for the front writer
task in the waitqueue.
Yuanhan Liu implemented lock-stealing for spinlock-rwsems,
which indeed recovered much of the regression - confirming
the analysis that the main factor in the regression was the
FIFO writer-fairness of rwsems.
In this patch we allow lock-stealing to happen when the first
waiter is also writer. With that change in place the
aim7 fork_test performance is fully recovered on my
Intel NHM EP, NHM EX, SNB EP 2S and 4S test-machines.
Reported-by: lkp@linux.intel.com
Reported-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Signed-off-by: Alex Shi <alex.shi@intel.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Anton Blanchard <anton@samba.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: paul.gortmaker@windriver.com
Link: https://lkml.org/lkml/2013/1/29/84
Link: http://lkml.kernel.org/r/1360069915-31619-1-git-send-email-alex.shi@intel.com
[ Small stylistic fixes, updated changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
300 lines
8.5 KiB
C
300 lines
8.5 KiB
C
/* rwsem.c: R/W semaphores: contention handling functions
|
|
*
|
|
* Written by David Howells (dhowells@redhat.com).
|
|
* Derived from arch/i386/kernel/semaphore.c
|
|
*
|
|
* Writer lock-stealing by Alex Shi <alex.shi@intel.com>
|
|
*/
|
|
#include <linux/rwsem.h>
|
|
#include <linux/sched.h>
|
|
#include <linux/init.h>
|
|
#include <linux/export.h>
|
|
|
|
/*
|
|
* Initialize an rwsem:
|
|
*/
|
|
void __init_rwsem(struct rw_semaphore *sem, const char *name,
|
|
struct lock_class_key *key)
|
|
{
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
/*
|
|
* Make sure we are not reinitializing a held semaphore:
|
|
*/
|
|
debug_check_no_locks_freed((void *)sem, sizeof(*sem));
|
|
lockdep_init_map(&sem->dep_map, name, key, 0);
|
|
#endif
|
|
sem->count = RWSEM_UNLOCKED_VALUE;
|
|
raw_spin_lock_init(&sem->wait_lock);
|
|
INIT_LIST_HEAD(&sem->wait_list);
|
|
}
|
|
|
|
EXPORT_SYMBOL(__init_rwsem);
|
|
|
|
struct rwsem_waiter {
|
|
struct list_head list;
|
|
struct task_struct *task;
|
|
unsigned int flags;
|
|
#define RWSEM_WAITING_FOR_READ 0x00000001
|
|
#define RWSEM_WAITING_FOR_WRITE 0x00000002
|
|
};
|
|
|
|
/* Wake types for __rwsem_do_wake(). Note that RWSEM_WAKE_NO_ACTIVE and
|
|
* RWSEM_WAKE_READ_OWNED imply that the spinlock must have been kept held
|
|
* since the rwsem value was observed.
|
|
*/
|
|
#define RWSEM_WAKE_ANY 0 /* Wake whatever's at head of wait list */
|
|
#define RWSEM_WAKE_NO_ACTIVE 1 /* rwsem was observed with no active thread */
|
|
#define RWSEM_WAKE_READ_OWNED 2 /* rwsem was observed to be read owned */
|
|
|
|
/*
|
|
* handle the lock release when processes blocked on it that can now run
|
|
* - if we come here from up_xxxx(), then:
|
|
* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
|
|
* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
|
|
* - there must be someone on the queue
|
|
* - the spinlock must be held by the caller
|
|
* - woken process blocks are discarded from the list after having task zeroed
|
|
* - writers are only woken if downgrading is false
|
|
*/
|
|
static struct rw_semaphore *
|
|
__rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
|
|
{
|
|
struct rwsem_waiter *waiter;
|
|
struct task_struct *tsk;
|
|
struct list_head *next;
|
|
signed long woken, loop, adjustment;
|
|
|
|
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
|
|
if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
|
|
goto readers_only;
|
|
|
|
if (wake_type == RWSEM_WAKE_READ_OWNED)
|
|
/* Another active reader was observed, so wakeup is not
|
|
* likely to succeed. Save the atomic op.
|
|
*/
|
|
goto out;
|
|
|
|
/* Wake up the writing waiter and let the task grab the sem: */
|
|
wake_up_process(waiter->task);
|
|
goto out;
|
|
|
|
readers_only:
|
|
/* If we come here from up_xxxx(), another thread might have reached
|
|
* rwsem_down_failed_common() before we acquired the spinlock and
|
|
* woken up a waiter, making it now active. We prefer to check for
|
|
* this first in order to not spend too much time with the spinlock
|
|
* held if we're not going to be able to wake up readers in the end.
|
|
*
|
|
* Note that we do not need to update the rwsem count: any writer
|
|
* trying to acquire rwsem will run rwsem_down_write_failed() due
|
|
* to the waiting threads and block trying to acquire the spinlock.
|
|
*
|
|
* We use a dummy atomic update in order to acquire the cache line
|
|
* exclusively since we expect to succeed and run the final rwsem
|
|
* count adjustment pretty soon.
|
|
*/
|
|
if (wake_type == RWSEM_WAKE_ANY &&
|
|
rwsem_atomic_update(0, sem) < RWSEM_WAITING_BIAS)
|
|
/* Someone grabbed the sem for write already */
|
|
goto out;
|
|
|
|
/* Grant an infinite number of read locks to the readers at the front
|
|
* of the queue. Note we increment the 'active part' of the count by
|
|
* the number of readers before waking any processes up.
|
|
*/
|
|
woken = 0;
|
|
do {
|
|
woken++;
|
|
|
|
if (waiter->list.next == &sem->wait_list)
|
|
break;
|
|
|
|
waiter = list_entry(waiter->list.next,
|
|
struct rwsem_waiter, list);
|
|
|
|
} while (waiter->flags & RWSEM_WAITING_FOR_READ);
|
|
|
|
adjustment = woken * RWSEM_ACTIVE_READ_BIAS;
|
|
if (waiter->flags & RWSEM_WAITING_FOR_READ)
|
|
/* hit end of list above */
|
|
adjustment -= RWSEM_WAITING_BIAS;
|
|
|
|
rwsem_atomic_add(adjustment, sem);
|
|
|
|
next = sem->wait_list.next;
|
|
for (loop = woken; loop > 0; loop--) {
|
|
waiter = list_entry(next, struct rwsem_waiter, list);
|
|
next = waiter->list.next;
|
|
tsk = waiter->task;
|
|
smp_mb();
|
|
waiter->task = NULL;
|
|
wake_up_process(tsk);
|
|
put_task_struct(tsk);
|
|
}
|
|
|
|
sem->wait_list.next = next;
|
|
next->prev = &sem->wait_list;
|
|
|
|
out:
|
|
return sem;
|
|
}
|
|
|
|
/* Try to get write sem, caller holds sem->wait_lock: */
|
|
static int try_get_writer_sem(struct rw_semaphore *sem,
|
|
struct rwsem_waiter *waiter)
|
|
{
|
|
struct rwsem_waiter *fwaiter;
|
|
long oldcount, adjustment;
|
|
|
|
/* only steal when first waiter is writing */
|
|
fwaiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
|
|
if (!(fwaiter->flags & RWSEM_WAITING_FOR_WRITE))
|
|
return 0;
|
|
|
|
adjustment = RWSEM_ACTIVE_WRITE_BIAS;
|
|
/* Only one waiter in the queue: */
|
|
if (fwaiter == waiter && waiter->list.next == &sem->wait_list)
|
|
adjustment -= RWSEM_WAITING_BIAS;
|
|
|
|
try_again_write:
|
|
oldcount = rwsem_atomic_update(adjustment, sem) - adjustment;
|
|
if (!(oldcount & RWSEM_ACTIVE_MASK)) {
|
|
/* No active lock: */
|
|
struct task_struct *tsk = waiter->task;
|
|
|
|
list_del(&waiter->list);
|
|
smp_mb();
|
|
put_task_struct(tsk);
|
|
tsk->state = TASK_RUNNING;
|
|
return 1;
|
|
}
|
|
/* some one grabbed the sem already */
|
|
if (rwsem_atomic_update(-adjustment, sem) & RWSEM_ACTIVE_MASK)
|
|
return 0;
|
|
goto try_again_write;
|
|
}
|
|
|
|
/*
|
|
* wait for a lock to be granted
|
|
*/
|
|
static struct rw_semaphore __sched *
|
|
rwsem_down_failed_common(struct rw_semaphore *sem,
|
|
unsigned int flags, signed long adjustment)
|
|
{
|
|
struct rwsem_waiter waiter;
|
|
struct task_struct *tsk = current;
|
|
signed long count;
|
|
|
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
|
|
/* set up my own style of waitqueue */
|
|
raw_spin_lock_irq(&sem->wait_lock);
|
|
waiter.task = tsk;
|
|
waiter.flags = flags;
|
|
get_task_struct(tsk);
|
|
|
|
if (list_empty(&sem->wait_list))
|
|
adjustment += RWSEM_WAITING_BIAS;
|
|
list_add_tail(&waiter.list, &sem->wait_list);
|
|
|
|
/* we're now waiting on the lock, but no longer actively locking */
|
|
count = rwsem_atomic_update(adjustment, sem);
|
|
|
|
/* If there are no active locks, wake the front queued process(es) up.
|
|
*
|
|
* Alternatively, if we're called from a failed down_write(), there
|
|
* were already threads queued before us and there are no active
|
|
* writers, the lock must be read owned; so we try to wake any read
|
|
* locks that were queued ahead of us. */
|
|
if (count == RWSEM_WAITING_BIAS)
|
|
sem = __rwsem_do_wake(sem, RWSEM_WAKE_NO_ACTIVE);
|
|
else if (count > RWSEM_WAITING_BIAS &&
|
|
adjustment == -RWSEM_ACTIVE_WRITE_BIAS)
|
|
sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED);
|
|
|
|
raw_spin_unlock_irq(&sem->wait_lock);
|
|
|
|
/* wait to be given the lock */
|
|
for (;;) {
|
|
if (!waiter.task)
|
|
break;
|
|
|
|
raw_spin_lock_irq(&sem->wait_lock);
|
|
/* Try to get the writer sem, may steal from the head writer: */
|
|
if (flags == RWSEM_WAITING_FOR_WRITE)
|
|
if (try_get_writer_sem(sem, &waiter)) {
|
|
raw_spin_unlock_irq(&sem->wait_lock);
|
|
return sem;
|
|
}
|
|
raw_spin_unlock_irq(&sem->wait_lock);
|
|
schedule();
|
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
}
|
|
|
|
tsk->state = TASK_RUNNING;
|
|
|
|
return sem;
|
|
}
|
|
|
|
/*
|
|
* wait for the read lock to be granted
|
|
*/
|
|
struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
|
|
{
|
|
return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_READ,
|
|
-RWSEM_ACTIVE_READ_BIAS);
|
|
}
|
|
|
|
/*
|
|
* wait for the write lock to be granted
|
|
*/
|
|
struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
|
|
{
|
|
return rwsem_down_failed_common(sem, RWSEM_WAITING_FOR_WRITE,
|
|
-RWSEM_ACTIVE_WRITE_BIAS);
|
|
}
|
|
|
|
/*
|
|
* handle waking up a waiter on the semaphore
|
|
* - up_read/up_write has decremented the active part of count if we come here
|
|
*/
|
|
struct rw_semaphore *rwsem_wake(struct rw_semaphore *sem)
|
|
{
|
|
unsigned long flags;
|
|
|
|
raw_spin_lock_irqsave(&sem->wait_lock, flags);
|
|
|
|
/* do nothing if list empty */
|
|
if (!list_empty(&sem->wait_list))
|
|
sem = __rwsem_do_wake(sem, RWSEM_WAKE_ANY);
|
|
|
|
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
|
|
|
|
return sem;
|
|
}
|
|
|
|
/*
|
|
* downgrade a write lock into a read lock
|
|
* - caller incremented waiting part of count and discovered it still negative
|
|
* - just wake up any readers at the front of the queue
|
|
*/
|
|
struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
|
|
{
|
|
unsigned long flags;
|
|
|
|
raw_spin_lock_irqsave(&sem->wait_lock, flags);
|
|
|
|
/* do nothing if list empty */
|
|
if (!list_empty(&sem->wait_list))
|
|
sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED);
|
|
|
|
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
|
|
|
|
return sem;
|
|
}
|
|
|
|
EXPORT_SYMBOL(rwsem_down_read_failed);
|
|
EXPORT_SYMBOL(rwsem_down_write_failed);
|
|
EXPORT_SYMBOL(rwsem_wake);
|
|
EXPORT_SYMBOL(rwsem_downgrade_wake);
|