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From: Ingo Molnar <mingo@kernel.org>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>,
	Michel Lespinasse <walken@google.com>,
	Davidlohr Bueso <davidlohr.bueso@hp.com>,
	Matthew R Wilcox <matthew.r.wilcox@intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Rik van Riel <riel@redhat.com>,
	Peter Hurley <peter@hurleysoftware.com>,
	linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file
Date: Thu, 26 Sep 2013 08:46:29 +0200	[thread overview]
Message-ID: <20130926064629.GB19090@gmail.com> (raw)
In-Reply-To: <1380147049.3467.67.camel@schen9-DESK>


* Tim Chen <tim.c.chen@linux.intel.com> wrote:

> We will need the MCS lock code for doing optimistic spinning for rwsem.
> Extracting the MCS code from mutex.c and put into its own file allow us
> to reuse this code easily for rwsem.
> 
> Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
> Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
> ---
>  include/linux/mcslock.h |   58 +++++++++++++++++++++++++++++++++++++++++++++++
>  kernel/mutex.c          |   58 +++++-----------------------------------------
>  2 files changed, 65 insertions(+), 51 deletions(-)
>  create mode 100644 include/linux/mcslock.h
> 
> diff --git a/include/linux/mcslock.h b/include/linux/mcslock.h
> new file mode 100644
> index 0000000..20fd3f0
> --- /dev/null
> +++ b/include/linux/mcslock.h
> @@ -0,0 +1,58 @@
> +/*
> + * MCS lock defines
> + *
> + * This file contains the main data structure and API definitions of MCS lock.

A (very) short blurb about what an MCS lock is would be nice here.

> + */
> +#ifndef __LINUX_MCSLOCK_H
> +#define __LINUX_MCSLOCK_H
> +
> +struct mcs_spin_node {
> +	struct mcs_spin_node *next;
> +	int		  locked;	/* 1 if lock acquired */
> +};

The vertical alignment looks broken here.

> +
> +/*
> + * We don't inline mcs_spin_lock() so that perf can correctly account for the
> + * time spent in this lock function.
> + */
> +static noinline
> +void mcs_spin_lock(struct mcs_spin_node **lock, struct mcs_spin_node *node)
> +{
> +	struct mcs_spin_node *prev;
> +
> +	/* Init node */
> +	node->locked = 0;
> +	node->next   = NULL;
> +
> +	prev = xchg(lock, node);
> +	if (likely(prev == NULL)) {
> +		/* Lock acquired */
> +		node->locked = 1;
> +		return;
> +	}
> +	ACCESS_ONCE(prev->next) = node;
> +	smp_wmb();
> +	/* Wait until the lock holder passes the lock down */
> +	while (!ACCESS_ONCE(node->locked))
> +		arch_mutex_cpu_relax();
> +}
> +
> +static void mcs_spin_unlock(struct mcs_spin_node **lock, struct mcs_spin_node *node)
> +{
> +	struct mcs_spin_node *next = ACCESS_ONCE(node->next);
> +
> +	if (likely(!next)) {
> +		/*
> +		 * Release the lock by setting it to NULL
> +		 */
> +		if (cmpxchg(lock, node, NULL) == node)
> +			return;
> +		/* Wait until the next pointer is set */
> +		while (!(next = ACCESS_ONCE(node->next)))
> +			arch_mutex_cpu_relax();
> +	}
> +	ACCESS_ONCE(next->locked) = 1;
> +	smp_wmb();
> +}
> +
> +#endif

We typically close header guards not via a plain #endif but like this:

#endif /* __LINUX_SPINLOCK_H */

#endif /* __LINUX_SPINLOCK_TYPES_H */

etc.

Thanks,

	Ingo

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  reply	other threads:[~2013-09-26  6:46 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <cover.1380144003.git.tim.c.chen@linux.intel.com>
2013-09-25 22:10 ` [PATCH v6 0/6] rwsem: performance optimizations Tim Chen
2013-09-25 22:10 ` [PATCH v6 1/6] rwsem: check the lock before cpmxchg in down_write_trylock Tim Chen
2013-09-25 22:10 ` [PATCH v6 2/6] rwsem: remove 'out' label in do_wake Tim Chen
2013-09-25 22:10 ` [PATCH v6 3/6] rwsem: remove try_reader_grant label do_wake Tim Chen
2013-09-25 22:10 ` [PATCH v6 4/6] rwsem/wake: check lock before do atomic update Tim Chen
2013-09-25 22:10 ` [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file Tim Chen
2013-09-26  6:46   ` Ingo Molnar [this message]
2013-09-26  8:40     ` Peter Zijlstra
2013-09-26  9:37       ` Ingo Molnar
2013-09-26 18:18       ` Tim Chen
2013-09-26 19:27   ` Jason Low
2013-09-26 20:06     ` Davidlohr Bueso
2013-09-26 20:23       ` Jason Low
2013-09-26 20:40         ` Davidlohr Bueso
2013-09-26 21:09           ` Jason Low
2013-09-26 21:41             ` Tim Chen
2013-09-26 22:42               ` Jason Low
2013-09-26 22:57                 ` Tim Chen
2013-09-27  6:02                   ` Ingo Molnar
2013-09-27  6:26                     ` Jason Low
2013-09-27 11:23                     ` Peter Zijlstra
2013-09-27 13:44                       ` Joe Perches
2013-09-27 13:48                         ` Peter Zijlstra
2013-09-27 14:05                           ` Joe Perches
2013-09-27 14:18                             ` Peter Zijlstra
2013-09-27 14:14                           ` [PATCH] checkpatch: Make the memory barrier test noisier Joe Perches
2013-09-27 14:26                             ` Peter Zijlstra
2013-09-27 14:34                               ` Joe Perches
2013-09-27 14:50                                 ` Peter Zijlstra
2013-09-27 15:17                                   ` Paul E. McKenney
2013-09-27 15:34                                     ` Peter Zijlstra
2013-09-27 16:04                                       ` Paul E. McKenney
2013-09-27 23:40                                   ` Oliver Neukum
2013-09-28  7:54                                     ` Peter Zijlstra
2013-09-27 16:12                     ` [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines and locking code into its own file Jason Low
2013-09-27 16:19                       ` Tim Chen
2013-10-02 19:19                 ` Waiman Long
2013-10-02 19:30                   ` Jason Low
2013-10-02 19:37                     ` Waiman Long
2013-09-26 22:22             ` Davidlohr Bueso
2013-09-27 15:29   ` Paul E. McKenney
2013-09-27 18:09     ` Tim Chen
2013-09-28  2:58       ` Waiman Long
2013-09-27 19:38     ` Tim Chen
2013-09-27 20:16       ` Jason Low
2013-09-27 20:38       ` Paul E. McKenney
2013-09-27 22:46         ` Tim Chen
2013-09-27 23:01           ` Paul E. McKenney
2013-09-27 23:54             ` Jason Low
2013-09-28  0:02               ` Davidlohr Bueso
2013-09-28  2:19               ` Paul E. McKenney
2013-09-28  4:34                 ` Jason Low
2013-09-30 15:51                   ` Waiman Long
2013-09-30 16:10                     ` Jason Low
2013-09-30 16:36                       ` Waiman Long
2013-10-01 16:48                         ` Tim Chen
2013-10-01 20:01                           ` Waiman Long
2013-10-01 21:16                             ` Tim Chen
2013-10-02  1:25                               ` Waiman Long
2013-10-02 18:43                                 ` Tim Chen
2013-10-02 19:32                                   ` Waiman Long
2013-09-30 16:28                 ` Tim Chen
2013-09-25 22:10 ` [PATCH v6 6/6] rwsem: do optimistic spinning for writer lock acquisition Tim Chen
2013-09-26  6:53   ` Ingo Molnar

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