linux-kernel - Re: [RFC][RT][PATCH 3/4] rtmutex: Revert Optimize rt lock wakeup

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Message-ID: <1294086147.3948.194.camel@gandalf.stny.rr.com>
Date:	Mon, 03 Jan 2011 15:22:27 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	ThomasGleixner <tglx@...utronix.de>,
	Peter Morreale <PMorreale@...ell.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][RT][PATCH 3/4] rtmutex: Revert Optimize rt lock wakeup

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
> 


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