This is a nasty interface and setting the state of a foreign task must
not be done. As of the following commit:
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. An important arch that is affected is arm64, however this has
been addressed now [1] and performance is up to par making no difference
with either calls.
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.
[1] https://lkml.kernel.org/r/
1483468021-8237-1-git-send-email-mark.rutland@arm.com
== 1. x86-64 ==
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%)
== 2. 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%)
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.
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.
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Cc: mark.rutland@arm.com
Link: http://lkml.kernel.org/r/1483479794-14013-5-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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);
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();
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;
static void __wait(struct waiter *w)
{
for (;;) {
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!w->task)
break;
schedule();
}
- set_task_state(current, TASK_RUNNING);
+ set_current_state(TASK_RUNNING);
}
static void __wake_waiter(struct waiter *w)
libcfs_debug_dumplog();
if (libcfs_panic_on_lbug)
panic("LBUG");
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
while (1)
schedule();
}
/* wait to be given the lock */
for (;;) {
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!waiter.task)
break;
timeout = schedule_timeout(timeout);
}
- __set_task_state(current, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
if (!timeout) {
/* lock timed out but check if this task was just
waiter.task = current;
- set_task_state(current, 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(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
locked = writer_trylock(sem);
if (locked)
break;
list_del(&waiter.list);
raw_spin_unlock_irq(&sem->wait_lock);
- __set_task_state(current, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
/* lock wait may have timed out */
if (!locked)
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)
#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_; \
} 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
complete(&core_state->startup);
for (;;) {
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!self.task) /* see coredump_finish() */
break;
freezable_schedule();
}
- __set_task_state(current, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
down_read(&mm->mmap_sem);
}
atomic_inc(&mm->mm_count);
lock_contended(&lock->dep_map, ip);
- set_task_state(current, state);
+ set_current_state(state);
for (;;) {
/*
* Once we hold wait_lock, we're serialized against
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
}
- set_task_state(current, 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(),
}
spin_lock_mutex(&lock->wait_lock, flags);
acquired:
- __set_task_state(current, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, current);
if (likely(list_empty(&lock->wait_list)))
return 0;
err:
- __set_task_state(current, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, current);
spin_unlock_mutex(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
goto out;
}
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
/* set up my own style of waitqueue */
waiter.task = current;
if (!waiter.task)
break;
schedule();
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
}
- __set_task_state(current, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
out:
;
}
ret = -EINTR;
goto out;
}
- set_task_state(current, state);
+ set_current_state(state);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
schedule();
raw_spin_lock_irqsave(&sem->wait_lock, flags);
/* wait to be given the lock */
while (true) {
- set_task_state(current, TASK_UNINTERRUPTIBLE);
+ set_current_state(TASK_UNINTERRUPTIBLE);
if (!waiter.task)
break;
schedule();
}
- __set_task_state(current, TASK_RUNNING);
+ __set_current_state(TASK_RUNNING);
return sem;
}
EXPORT_SYMBOL(rwsem_down_read_failed);
goto interrupted;
if (unlikely(timeout <= 0))
goto timed_out;
- __set_task_state(current, state);
+ __set_current_state(state);
raw_spin_unlock_irq(&sem->lock);
timeout = schedule_timeout(timeout);
raw_spin_lock_irq(&sem->lock);
projects / GitHub / LineageOS / android_kernel_motorola_exynos9610.git / commitdiff