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Message-ID: <16879.29449.734172.893834@wombat.chubb.wattle.id.au>
Date: Thu, 20 Jan 2005 19:59:53 +1100
From: Peter Chubb <peterc@gelato.unsw.edu.au>
To: Chris Wedgwood <cw@f00f.org>
Cc: Andrew Morton <akpm@osdl.org>, paulus@samba.org,
       linux-kernel@vger.kernel.org, mingo@elte.hu, peterc@gelato.unsw.edu.au,
       tony.luck@intel.com, dsw@gelato.unsw.edu.au, torvalds@osdl.org,
       benh@kernel.crashing.org, linux-ia64@vger.kernel.org, hch@infradead.org,
       wli@holomorphy.com, jbarnes@sgi.com
Subject: Re: [PATCH RFC] 'spinlock/rwlock fixes' V3 [1/1]
In-Reply-To: <20050120031854.GA8538@taniwha.stupidest.org>
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>>>>> "Chris" == Chris Wedgwood <cw@f00f.org> writes:

Chris> On Wed, Jan 19, 2005 at 07:01:04PM -0800, Andrew Morton wrote:

Chris> It still isn't enough to rid of the rwlock_read_locked and
Chris> rwlock_write_locked usage in kernel/spinlock.c as those are
Chris> needed for the cpu_relax() calls so we have to decide on
Chris> suitable names still...  

I suggest reversing the sense of the macros, and having read_can_lock()
and write_can_lock()

Meaning:
	read_can_lock() --- a read_lock() would have succeeded
	write_can_lock() --- a write_lock() would have succeeded.

IA64 implementation:

#define read_can_lock(x)  (*(volatile int *)x >= 0)
#define write_can_lock(x) (*(volatile int *)x == 0)

Then use them as
     !read_can_lock(x)
where you want the old semantics.  The compiler ought to be smart
enough to optimise the boolean ops.

---
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
The technical we do immediately,  the political takes *forever*


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