From mboxrd@z Thu Jan  1 00:00:00 1970
From: Lai Jiangshan <laijs@cn.fujitsu.com>
Subject: Re: [PATCH][RFC]: mutex: adaptive spin
Date: Wed, 07 Jan 2009 11:57:29 +0800
Message-ID: <49642829.20006@cn.fujitsu.com>
References: <87r63ljzox.fsf@basil.nowhere.org>	 <20090103191706.GA2002@parisc-linux.org> <1231093310.27690.5.camel@twins>	 <20090104184103.GE2002@parisc-linux.org> <1231242031.11687.97.camel@twins>	 <20090106121052.GA27232@elte.hu> <4963584A.4090805@novell.com>	 <20090106131643.GA15228@elte.hu> <1231248041.11687.107.camel@twins>	 <49636799.1010109@novell.com>  <20090106214229.GD6741@linux.vnet.ibm.com>	 <1231278275.11687.111.camel@twins>	 <alpine.LFD.2.00.0901061349520.3057@localhost.localdomain>	 <1231279660.11687.121.camel@twins>	 <alpine.LFD.2.00.0901061413310.3057@localhost.localdomain> <1231281801.11687.125.camel@twins>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	paulmck@linux.vnet.ibm.com, Gregory Haskins <ghaskins@novell.com>,
	Ingo Molnar <mingo@elte.hu>, Matthew Wilcox <matthew@wil.cx>,
	Andi Kleen <andi@firstfloor.org>,
	Chris Mason <chris.mason@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Nick Piggin <npiggin@suse.de>,
	Peter Morreale <pmorreale@novell.com>,
	Sven Dietrich <SDietrich@novell.com>
To: Peter Zijlstra <peterz@infradead.org>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
In-Reply-To: <1231281801.11687.125.camel@twins>
List-ID: <linux-btrfs.vger.kernel.org>

Peter Zijlstra wrote:
> +void mutex_spin_or_schedule(struct mutex_waiter *waiter, long state, unsigned long *flags)
> +{
> +	struct mutex *lock = waiter->lock;
> +	struct task_struct *task = waiter->task;
> +	struct task_struct *owner = lock->owner;
> +	struct rq *rq;
> +
> +	if (!owner)
> +		goto do_schedule;
> +
> +	rq = task_rq(owner);
> +
> +	if (rq->curr != owner) {
> +do_schedule:
> +		__set_task_state(task, state);
> +		spin_unlock_mutex(&lock->wait_lock, *flags);
> +		schedule();
> +	} else {
> +		spin_unlock_mutex(&lock->wait_lock, *flags);
> +		for (;;) {
> +			/* Stop spinning when there's a pending signal. */
> +			if (signal_pending_state(state, task))
> +				break;
> +
> +			/* Owner changed, bail to revalidate state */
> +			if (lock->owner != owner)
> +				break;
> +
> +			/* Owner stopped running, bail to revalidate state */
> +			if (rq->curr != owner)
> +				break;
> +

2 questions from my immature thought:

1) Do we need keep gcc from optimizing when we access lock->owner
   and rq->curr in the loop?

2) "if (rq->curr != owner)" need become smarter.
   schedule()
   {
	select_next
	rq->curr = next;
	contex_swith
   }
we also spin when owner is select_next-ing in schedule().
but select_next is not fast enough.


Lai.