@@ -76,7 +76,7 @@ static ssize_t rng_dev_read (struct file *filp, char __user *buf, size_t size,
add_sigio_fd(random_fd);
add_wait_queue(&host_read_wait, &wait);
- set_task_state(current, TASK_INTERRUPTIBLE);
+ set_current_state(TASK_INTERRUPTIBLE);
schedule();
remove_wait_queue(&host_read_wait, &wait);
@@ -794,7 +794,7 @@ static void __wait_for_free_buffer(struct dm_bufio_client *c)
DECLARE_WAITQUEUE(wait, current);
add_wait_queue(&c->free_buffer_wait, &wait);
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
dm_bufio_unlock(c);
io_schedule();
@@ -1210,14 +1210,14 @@ static int dmcrypt_write(void *data)
spin_unlock_irq(&cc->write_thread_wait.lock);
if (unlikely(kthread_should_stop())) {
- set_task_state(current, TASK_RUNNING);
+ set_current_state(TASK_RUNNING);
remove_wait_queue(&cc->write_thread_wait, &wait);
break;
}
schedule();
- set_task_state(current, TASK_RUNNING);
+ set_current_state(TASK_RUNNING);
spin_lock_irq(&cc->write_thread_wait.lock);
__remove_wait_queue(&cc->write_thread_wait, &wait);
goto continue_locked;
@@ -120,7 +120,7 @@ static int __check_holder(struct block_lock *lock)
static void __wait(struct waiter *w)
{
for (;;) {
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!w->task)
break;
@@ -128,7 +128,7 @@ static void __wait(struct waiter *w)
schedule();
}
- set_task_state(current, TASK_RUNNING);
+ set_current_state(TASK_RUNNING);
}
static void __wake_waiter(struct waiter *w)
@@ -107,7 +107,7 @@ void __noreturn lbug_with_loc(struct libcfs_debug_msg_data *msgdata)
libcfs_debug_dumplog();
if (libcfs_panic_on_lbug)
panic("LBUG");
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
while (1)
schedule();
}
@@ -232,7 +232,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout)
/* wait to be given the lock */
for (;;) {
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!waiter.task)
break;
@@ -241,7 +241,7 @@ down_read_failed(struct ld_semaphore *sem, long count, long timeout)
timeout = schedule_timeout(timeout);
}
- __set_task_state(tsk, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
if (!timeout) {
/* lock timed out but check if this task was just
@@ -291,14 +291,14 @@ down_write_failed(struct ld_semaphore *sem, long count, long timeout)
waiter.task = tsk;
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
for (;;) {
if (!timeout)
break;
raw_spin_unlock_irq(&sem->wait_lock);
timeout = schedule_timeout(timeout);
raw_spin_lock_irq(&sem->wait_lock);
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
locked = writer_trylock(sem);
if (locked)
break;
@@ -309,7 +309,7 @@ down_write_failed(struct ld_semaphore *sem, long count, long timeout)
list_del(&waiter.list);
raw_spin_unlock_irq(&sem->wait_lock);
- __set_task_state(tsk, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
/* lock wait may have timed out */
if (!locked)
@@ -227,7 +227,7 @@ extern void proc_sched_set_task(struct task_struct *p);
extern char ___assert_task_state[1 - 2*!!(
sizeof(TASK_STATE_TO_CHAR_STR)-1 != ilog2(TASK_STATE_MAX)+1)];
-/* Convenience macros for the sake of set_task_state */
+/* Convenience macros for the sake of set_current_state */
#define TASK_KILLABLE (TASK_WAKEKILL | TASK_UNINTERRUPTIBLE)
#define TASK_STOPPED (TASK_WAKEKILL | __TASK_STOPPED)
#define TASK_TRACED (TASK_WAKEKILL | __TASK_TRACED)
@@ -254,17 +254,6 @@ extern char ___assert_task_state[1 - 2*!!(
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
-#define __set_task_state(tsk, state_value) \
- do { \
- (tsk)->task_state_change = _THIS_IP_; \
- (tsk)->state = (state_value); \
- } while (0)
-#define set_task_state(tsk, state_value) \
- do { \
- (tsk)->task_state_change = _THIS_IP_; \
- smp_store_mb((tsk)->state, (state_value)); \
- } while (0)
-
#define __set_current_state(state_value) \
do { \
current->task_state_change = _THIS_IP_; \
@@ -277,20 +266,6 @@ extern char ___assert_task_state[1 - 2*!!(
} while (0)
#else
-
-/*
- * @tsk had better be current, or you get to keep the pieces.
- *
- * The only reason is that computing current can be more expensive than
- * using a pointer that's already available.
- *
- * Therefore, see set_current_state().
- */
-#define __set_task_state(tsk, state_value) \
- do { (tsk)->state = (state_value); } while (0)
-#define set_task_state(tsk, state_value) \
- smp_store_mb((tsk)->state, (state_value))
-
/*
* set_current_state() includes a barrier so that the write of current->state
* is correctly serialised wrt the caller's subsequent test of whether to
@@ -501,12 +501,12 @@ static void exit_mm(struct task_struct *tsk)
complete(&core_state->startup);
for (;;) {
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!self.task) /* see coredump_finish() */
break;
freezable_schedule();
}
- __set_task_state(tsk, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
down_read(&mm->mmap_sem);
}
atomic_inc(&mm->mm_count);
@@ -667,7 +667,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
lock_contended(&lock->dep_map, ip);
- set_task_state(task, state);
+ set_current_state(state);
for (;;) {
/*
* Once we hold wait_lock, we're serialized against
@@ -702,7 +702,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
}
- set_task_state(task, state);
+ set_current_state(state);
/*
* Here we order against unlock; we must either see it change
* state back to RUNNING and fall through the next schedule(),
@@ -716,7 +716,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
}
spin_lock_mutex(&lock->wait_lock, flags);
acquired:
- __set_task_state(task, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, task);
if (likely(list_empty(&lock->wait_list)))
@@ -736,7 +736,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
return 0;
err:
- __set_task_state(task, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, task);
spin_unlock_mutex(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
@@ -141,7 +141,7 @@ void __sched __down_read(struct rw_semaphore *sem)
}
tsk = current;
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
/* set up my own style of waitqueue */
waiter.task = tsk;
@@ -158,10 +158,10 @@ void __sched __down_read(struct rw_semaphore *sem)
if (!waiter.task)
break;
schedule();
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
}
- __set_task_state(tsk, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
out:
;
}
@@ -220,7 +220,7 @@ int __sched __down_write_common(struct rw_semaphore *sem, int state)
ret = -EINTR;
goto out;
}
- set_task_state(tsk, state);
+ set_current_state(state);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
schedule();
raw_spin_lock_irqsave(&sem->wait_lock, flags);
@@ -254,13 +254,13 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
/* wait to be given the lock */
while (true) {
- set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!waiter.task)
break;
schedule();
}
- __set_task_state(tsk, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
return sem;
}
EXPORT_SYMBOL(rwsem_down_read_failed);
@@ -216,7 +216,7 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
goto interrupted;
if (unlikely(timeout <= 0))
goto timed_out;
- __set_task_state(task, state);
+ __set_current_state(state);
raw_spin_unlock_irq(&sem->lock);
timeout = schedule_timeout(timeout);
raw_spin_lock_irq(&sem->lock);
This is a nasty interface and setting the state of a foreign task must not be done. While as of be628be0956 (bcache: Make gc wakeup sane, remove set_task_state()) everyone in the kernel calls set_task_state() with current, allowing the helper to be removed. However, as the comment indicates, it is still around for those archs where computing current is more expensive than using a pointer, at least in theory. Of all the callers, if any, it's the locking bits that would care most about this -- ie: we end up passing a tsk pointer to a lot of the lock slowpath, and setting ->state on that. The following numbers are based on two tests: a custom ad-hoc microbenchmark that just measures latencies (for ~65 million calls) between get_task_state() vs get_current_state(). Secondly for a higher overview, an unlink microbenchmark was used, which pounds on a single file with open, close,unlink combos with increasing thread counts (up to 4x ncpus). While the workload is quite unrealistic, it does contend a lot on the inode mutex or now rwsem. With the archs I had access to, the differences are as follows: == 1. arm64 == 0000000000002784 <set_task_state>: 2784: f9000c1f str xzr, [x0,#24] 0000000000002790 <set_current_state>: 2790: d5384100 mrs x0, sp_el0 2794: f9000c1f str xzr, [x0,#24] Avg runtime set_task_state(): 2648 msecs Avg runtime set_current_state(): 2686 msecs vanilla dirty Hmean unlink1-processes-2 8146.94 ( 0.00%) 9564.74 ( 17.40%) Hmean unlink1-processes-5 9627.49 ( 0.00%) 8935.47 ( -7.19%) Hmean unlink1-processes-8 9148.07 ( 0.00%) 8867.29 ( -3.07%) Hmean unlink1-processes-12 9168.15 ( 0.00%) 8952.79 ( -2.35%) Hmean unlink1-processes-21 9067.45 ( 0.00%) 9246.20 ( 1.97%) Hmean unlink1-processes-30 9310.21 ( 0.00%) 8831.77 ( -5.14%) Hmean unlink1-processes-48 9100.57 ( 0.00%) 9084.36 ( -0.18%) Hmean unlink1-processes-79 9022.37 ( 0.00%) 8178.66 ( -9.35%) Hmean unlink1-processes-110 8940.33 ( 0.00%) 8186.77 ( -8.43%) Hmean unlink1-processes-141 9001.95 ( 0.00%) 8429.08 ( -6.36%) Hmean unlink1-processes-172 8990.60 ( 0.00%) 8059.33 (-10.36%) Hmean unlink1-processes-203 8456.43 ( 0.00%) 8065.69 ( -4.62%) Hmean unlink1-processes-234 9020.57 ( 0.00%) 8495.15 ( -5.82%) Hmean unlink1-processes-265 8849.48 ( 0.00%) 8123.47 ( -8.20%) Hmean unlink1-processes-296 8890.80 ( 0.00%) 8272.24 ( -6.96%) Hmean unlink1-processes-327 8637.74 ( 0.00%) 8377.55 ( -3.01%) Hmean unlink1-processes-358 8690.21 ( 0.00%) 8492.25 ( -2.28%) Hmean unlink1-processes-384 8687.64 ( 0.00%) 8510.68 ( -2.04%) == 2. x86-64 == 0000000000002cc0 <set_task_state>: 2cc1: 48 c7 47 08 00 00 00 movq $0x0,0x8(%rdi) 2cc9: 48 89 e5 mov %rsp,%rbp 0000000000002cd0 <set_current_state>: 2cd1: 65 48 8b 04 25 00 00 mov %gs:0x0,%rax 2cda: 48 89 e5 mov %rsp,%rbp 2cdd: 48 c7 40 08 00 00 00 movq $0x0,0x8(%rax) Avg runtime set_task_state(): 601 msecs Avg runtime set_current_state(): 552 msecs vanilla dirty Hmean unlink1-processes-2 36089.26 ( 0.00%) 38977.33 ( 8.00%) Hmean unlink1-processes-5 28555.01 ( 0.00%) 29832.55 ( 4.28%) Hmean unlink1-processes-8 37323.75 ( 0.00%) 44974.57 ( 20.50%) Hmean unlink1-processes-12 43571.88 ( 0.00%) 44283.01 ( 1.63%) Hmean unlink1-processes-21 34431.52 ( 0.00%) 38284.45 ( 11.19%) Hmean unlink1-processes-30 34813.26 ( 0.00%) 37975.17 ( 9.08%) Hmean unlink1-processes-48 37048.90 ( 0.00%) 39862.78 ( 7.59%) Hmean unlink1-processes-79 35630.01 ( 0.00%) 36855.30 ( 3.44%) Hmean unlink1-processes-110 36115.85 ( 0.00%) 39843.91 ( 10.32%) Hmean unlink1-processes-141 32546.96 ( 0.00%) 35418.52 ( 8.82%) Hmean unlink1-processes-172 34674.79 ( 0.00%) 36899.21 ( 6.42%) Hmean unlink1-processes-203 37303.11 ( 0.00%) 36393.04 ( -2.44%) Hmean unlink1-processes-224 35712.13 ( 0.00%) 36685.96 ( 2.73%) == 3. ppc64le == Avg runtime set_task_state(): 938 msecs Avg runtime set_current_state: 940 msecs vanilla dirty Hmean unlink1-processes-2 19269.19 ( 0.00%) 30704.50 ( 59.35%) Hmean unlink1-processes-5 20106.15 ( 0.00%) 21804.15 ( 8.45%) Hmean unlink1-processes-8 17496.97 ( 0.00%) 17243.28 ( -1.45%) Hmean unlink1-processes-12 14224.15 ( 0.00%) 17240.21 ( 21.20%) Hmean unlink1-processes-21 14155.66 ( 0.00%) 15681.23 ( 10.78%) Hmean unlink1-processes-30 14450.70 ( 0.00%) 15995.83 ( 10.69%) Hmean unlink1-processes-48 16945.57 ( 0.00%) 16370.42 ( -3.39%) Hmean unlink1-processes-79 15788.39 ( 0.00%) 14639.27 ( -7.28%) Hmean unlink1-processes-110 14268.48 ( 0.00%) 14377.40 ( 0.76%) Hmean unlink1-processes-141 14023.65 ( 0.00%) 16271.69 ( 16.03%) Hmean unlink1-processes-172 13417.62 ( 0.00%) 16067.55 ( 19.75%) Hmean unlink1-processes-203 15293.08 ( 0.00%) 15440.40 ( 0.96%) Hmean unlink1-processes-234 13719.32 ( 0.00%) 16190.74 ( 18.01%) Hmean unlink1-processes-265 16400.97 ( 0.00%) 16115.22 ( -1.74%) Hmean unlink1-processes-296 14388.60 ( 0.00%) 16216.13 ( 12.70%) Hmean unlink1-processes-320 15771.85 ( 0.00%) 15905.96 ( 0.85%) Unsurprisingly, the big looser is arm64, due to the masking of sp_el0. otoh, x86-64 (known to be fast for get_current()/this_cpu_read_stable() caching) and ppc64 (with paca) show similar improvements in the unlink microbenches. x86's write latencies delta is similar to the opposite of arm64: 50ms vs -40ms, respectively. The small delta for ppc64 (2ms), does not represent the gains on the unlink runs. In the case of x86, there was a decent amount of variation in the latency runs, but always within a 20 to 50ms increase), ppc was more constant. So, do we want to get rid of the interface (and improve performance on other archs) at the expense of arm64? Can arm64 do better? Applies against v4.10-rc1. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> --- arch/um/drivers/random.c | 2 +- drivers/md/dm-bufio.c | 2 +- drivers/md/dm-crypt.c | 4 ++-- drivers/md/persistent-data/dm-block-manager.c | 4 ++-- .../staging/lustre/lnet/libcfs/linux/linux-debug.c | 2 +- drivers/tty/tty_ldsem.c | 10 ++++---- include/linux/sched.h | 27 +--------------------- kernel/exit.c | 4 ++-- kernel/locking/mutex.c | 8 +++---- kernel/locking/rwsem-spinlock.c | 8 +++---- kernel/locking/rwsem-xadd.c | 4 ++-- kernel/locking/semaphore.c | 2 +- 12 files changed, 26 insertions(+), 51 deletions(-)