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Subject: Re: [RFC][RT][PATCH 3/4] rtmutex: Revert Optimize rt lock wakeup
From: Steven Rostedt <rostedt@goodmis.org>
To: Gregory Haskins <ghaskins@novell.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>, Ingo Molnar <mingo@elte.hu>,
        Peter Zijlstra <peterz@infradead.org>,
        ThomasGleixner <tglx@linutronix.de>,
        Peter Morreale <PMorreale@novell.com>, linux-kernel@vger.kernel.org
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Date: Mon, 03 Jan 2011 15:22:27 -0500
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On Mon, 2011-01-03 at 14:06 -0500, Steven Rostedt wrote:

> 
> 	if (adaptive_wait(&waiter, orig_owner))
> 		sleep = 1;
> 	else
> 		sleep = 0;
> 
> 	if (sleep)


> 		raw_spin_lock(&lock->wait_lock);
> 		saved_state = rt_set_current_block_state(saved_state);
> 		if (!lock->owner && &waiter == rt_mutex_top_waiter(lock))
> 			sleep = 0;
> 		raw_spin_unlock(&lock->wait_lock);

I may be able to remove the above locks and replace it with:

	saved_state = rt_set_current_blocked_state(saved_state);
	if (orig_owner == rt_mutex_owner(lock))
		schedule_rt_mutex(lock);

-- Steve


> 		if (sleep)
> 			schedule_rt_mutex(lock);
> 		saved_state = rt_restore_current_blocked_state(saved_state);
> 	}
> 
> Otherwise we can risk the wakeup_next_waiter() missing the wakeup.
> 
> To clarify, we want the adaptive_wait() to run as TASK_RUNNING. Then if
> we must sleep, then we must set the state to TASK_UNINTERRUPTIBLE, test
> again if we can still the lock, and if not then sleep. Otherwise, if a
> wakeup happens just before we set the state to TASK_UNINTERRUPTIBLE,
> then we miss the wake up all together.
> 
> I can do this change, and see what impact it makes.
> 
> I'm also curious if this ever worked? If it did not, then are you sure
> your tests that show the benefit of it was true. I don't have a large
> scale box at my disposal ATM, so I can only see what this does on 4way
> machines.
> 
> -- Steve
>