Re: [RFC PATCH 2/3] rt-mutex: deboost priority conditionally when rt-mutex unlock

Hi Juri,

Do you know how to test the rt-mutex?

Regards

On 04/01/2017 01:37 PM, Alex Shi wrote:

Hi Juri & Mathieu,

Sorry, sent out a wrong version of this patch. The correct one as following: Would you like to review this small patchset?

Regards Alex

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From a9b9fdcb07bcfef969c1bd7c660063108e2e61c2 Mon Sep 17 00:00:00 2001 From: Alex Shi alex.shi@linaro.org Date: Fri, 31 Mar 2017 11:40:22 +0800 Subject: [RFC PATCH 2/3] rt-mutex: deboost priority conditionally when rt-mutex unlock

The rt_mutex_fastunlock() will deboost 'current' task when it should be. but the rt_mutex_slowunlock() function will set the 'deboost' flag unconditionally. That cause some unnecessary priority adjustment.

'current' release a lock, so 'current' is a higher prio task than the next top waiter, unless the current prio was gotten from this top waiter, iff so, we need to deboost 'current' after lock release.

Signed-off-by: Alex Shi alex.shi@linaro.org To: linux-kernel@vger.kernel.org To: Ingo Molnar mingo@redhat.com To: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de

---

kernel/locking/rtmutex.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 6edc32e..f283a12 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1037,10 +1037,11 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,

• Called with lock->wait_lock held and interrupts disabled.

*/ -static void mark_wakeup_next_waiter(struct wake_q_head *wake_q, +static bool mark_wakeup_next_waiter(struct wake_q_head *wake_q, struct rt_mutex *lock) { struct rt_mutex_waiter *waiter;

• bool deboost = false;

raw_spin_lock(&current->pi_lock); @@ -1055,6 +1056,15 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q, rt_mutex_dequeue_pi(current, waiter); /*

• * 'current' release this lock, so 'current' is a higher prio task
  

• * than the next top waiter, unless the current prio was gotten
  

• * from this top waiter, iff so, we need to deboost 'current'
  

• * after lock release.
  

• */
  

• if (current->prio == waiter->prio)

• deboost = true;
  

• /*
  • As we are waking up the top waiter, and the waiter stays
  • queued on the lock until it gets the lock, this lock
  • obviously has waiters. Just set the bit here and this has

@@ -1067,6 +1077,8 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q, raw_spin_unlock(&current->pi_lock); wake_q_add(wake_q, waiter->task);

• return deboost;

} /* @@ -1336,6 +1348,7 @@ static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock, struct wake_q_head *wake_q) { unsigned long flags;

• bool deboost = false;

/* irqsave required to support early boot calls */ raw_spin_lock_irqsave(&lock->wait_lock, flags); @@ -1389,12 +1402,12 @@ static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock, * * Queue the next waiter for wakeup once we release the wait_lock. */

• mark_wakeup_next_waiter(wake_q, lock);

• deboost = mark_wakeup_next_waiter(wake_q, lock);

raw_spin_unlock_irqrestore(&lock->wait_lock, flags); /* check PI boosting */

• return true;

• return deboost;

} /*