From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Ingo Molnar <mingo@elte.hu>
Cc: Nicolas Pitre <nico@cam.org>,
Arjan van de Ven <arjan@infradead.org>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: [patch 1/3] mutex subsystem: trylock
Date: Thu, 29 Dec 2005 20:01:38 +1100 [thread overview]
Message-ID: <43B3A5F2.5060903@yahoo.com.au> (raw)
In-Reply-To: <20051229083333.GA31003@elte.hu>
Ingo Molnar wrote:
> * Nicolas Pitre <nico@cam.org> wrote:
>>+ "1: ldrex %0, [%3] \n"
>>+ "subs %1, %0, #1 \n"
>>+ "strexeq %2, %1, [%3] \n"
>>+ "movlt %0, #0 \n"
>>+ "cmpeq %2, #0 \n"
>>+ "bgt 1b \n"
>
>
> so we are back to what is in essence a cmpxchg implementation?
>
FWIW, I still think we should go for an open-coded "cmpxchg" variant
for UP that disables preempt, and an atomic_cmpxchg variant for SMP.
- good generic implementations
- the UP version is faster than atomic_xchg for non preempt on ARM
- if you really are counting cycles, you'd probably have preempt off
- if you've got preempt on then the preempt_ operations in semaphores
would be the least of your worries (how about spinlocks?)
Rather than straight out introducing lots of ugliness and complexity
for something that actually slows down the speed critical !preempt
case (but is unlikely to be measurable either way).
--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com
next prev parent reply other threads:[~2005-12-29 9:01 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-23 16:16 [patch 00/11] mutex subsystem, -V7 Ingo Molnar
2005-12-24 5:15 ` Nicolas Pitre
2005-12-24 5:23 ` Nicolas Pitre
2005-12-26 19:24 ` Nicolas Pitre
2005-12-26 19:25 ` [patch 1/3] mutex subsystem: trylock Nicolas Pitre
2005-12-27 11:51 ` Ingo Molnar
2005-12-27 20:47 ` Nicolas Pitre
2005-12-28 7:48 ` Ingo Molnar
2005-12-28 8:13 ` Ingo Molnar
2005-12-28 16:29 ` Nicolas Pitre
2005-12-28 17:09 ` Ingo Molnar
2005-12-27 12:05 ` Arjan van de Ven
2005-12-27 13:15 ` Ingo Molnar
2005-12-29 4:06 ` Nicolas Pitre
2005-12-29 8:33 ` Ingo Molnar
2005-12-29 9:01 ` Nick Piggin [this message]
2005-12-29 17:15 ` Nicolas Pitre
2005-12-30 2:05 ` Nick Piggin
2005-12-29 16:46 ` Nicolas Pitre
2005-12-29 3:22 ` Nicolas Pitre
2005-12-26 19:25 ` [patch 2/3] mutex subsystem: fastpath inlining Nicolas Pitre
2005-12-27 11:55 ` Ingo Molnar
2005-12-27 21:59 ` Nicolas Pitre
2005-12-28 7:41 ` Ingo Molnar
2005-12-29 2:53 ` Nicolas Pitre
2005-12-29 8:41 ` Ingo Molnar
2006-01-06 21:20 ` Nicolas Pitre
2005-12-26 19:26 ` [patch 3/3] mutex subsystem: inline mutex_is_locked() Nicolas Pitre
2005-12-27 11:37 ` Ingo Molnar
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