linux-kernel - Re: [tip:locking/core] rwsem: Support optimistic spinning

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Date:	Mon, 19 May 2014 17:27:57 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	Jason Low <jason.low2@...com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Peter Hurley <peter@...leysoftware.com>,
	Alex Shi <alex.shi@...aro.org>, Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Norton, Scott J" <scott.norton@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Michel Lespinasse <walken@...gle.com>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:locking/core] rwsem: Support optimistic spinning

> So if given the choice between the 2, I think checking
> !CONFIG_RWSEM_GENERIC_SPINLOCK is better just because we use that to
> decide the implementation/structure layout.

Yeah, I suspect this is more suitable as well. Thanks.

8<---------------------------------------------
From: Davidlohr Bueso <davidlohr@...com>
Subject: [PATCH] rwsem: Fix warnings for CONFIG_RWSEM_GENERIC_SPINLOCK

Optimistic spinning is only used by the xadd variant
of rw-semaphores. Make sure that we use the old version
of the __RWSEM_INITIALIZER macro for systems that rely
on the spinlock one, otherwise warnings can be triggered,
such as the following reported on an arm box:

ipc/ipcns_notifier.c:22:8: warning: excess elements in struct initializer [enabled by default]
ipc/ipcns_notifier.c:22:8: warning: (near initialization for 'ipcns_chain.rwsem') [enabled by default]
ipc/ipcns_notifier.c:22:8: warning: excess elements in struct initializer [enabled by default]
ipc/ipcns_notifier.c:22:8: warning: (near initialization for 'ipcns_chain.rwsem') [enabled by default]

Signed-off-by: Davidlohr Bueso <davidlohr@...com>
---
 include/linux/rwsem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 3e108f1..8d79708 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -64,7 +64,7 @@ static inline int rwsem_is_locked(struct rw_semaphore *sem)
 # define __RWSEM_DEP_MAP_INIT(lockname)
 #endif
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) && !defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
 #define __RWSEM_INITIALIZER(name)			\
 	{ RWSEM_UNLOCKED_VALUE,				\
 	  __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),	\
-- 
1.8.1.4



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