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SubjectRe: [PATCH 2/2] locking: Apply contention tracepoints in the slow path
On Fri, Mar 18, 2022 at 08:55:32PM +0800, Boqun Feng wrote:
> On Wed, Mar 16, 2022 at 03:45:48PM -0700, Namhyung Kim wrote:
> [...]
> > @@ -209,6 +210,7 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
> > long timeout)
> > {
> > struct semaphore_waiter waiter;
> > + bool tracing = false;
> >
> > list_add_tail(&waiter.list, &sem->wait_list);
> > waiter.task = current;
> > @@ -220,18 +222,28 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
> > if (unlikely(timeout <= 0))
> > goto timed_out;
> > __set_current_state(state);
> > + if (!tracing) {
> > + trace_contention_begin(sem, 0);
>
> This looks a littl ugly ;-/ Maybe we can rename __down_common() to
> ___down_common() and implement __down_common() as:
>
> static inline int __sched __down_common(...)
> {
> int ret;
> trace_contention_begin(sem, 0);
> ret = ___down_common(...);
> trace_contention_end(sem, ret);
> return ret;
> }
>
> Thoughts?

Yeah, that works, except I think he wants a few extra
__set_current_state()'s like so:

diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index 9ee381e4d2a4..e2049a7e0ea4 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -205,8 +205,7 @@ struct semaphore_waiter {
* 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,
- long timeout)
+static __always_inline int ___down_common(struct semaphore *sem, long state, long timeout)
{
struct semaphore_waiter waiter;

@@ -227,15 +226,28 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
return 0;
}

- timed_out:
+timed_out:
list_del(&waiter.list);
return -ETIME;

- interrupted:
+interrupted:
list_del(&waiter.list);
return -EINTR;
}

+static __always_inline int __down_common(struct semaphore *sem, long state, long timeout)
+{
+ int ret;
+
+ __set_current_state(state);
+ trace_contention_begin(sem, 0);
+ ret = ___down_common(sem, state, timeout);
+ __set_current_state(TASK_RUNNING);
+ trace_contention_end(sem, ret);
+
+ return ret;
+}
+
static noinline void __sched __down(struct semaphore *sem)
{
__down_common(sem, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
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