From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Jeremy Fitzhardinge <jeremy@goop.org>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@elte.hu>, Joe Perches <joe@perches.com>,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC PATCH] Fair low-latency rwlock v5
Date: Tue, 19 Aug 2008 09:48:32 -0700 (PDT) [thread overview]
Message-ID: <alpine.LFD.1.10.0808190946560.3324@nehalem.linux-foundation.org> (raw)
In-Reply-To: <20080819073345.GA30285@Krystal>
On Tue, 19 Aug 2008, Mathieu Desnoyers wrote:
>
> It strikes me that Intel has a nice (probably slow?) cmpxchg16b
> instruction on x86_64. Therefore, we could atomically update 128 bits,
> which gives the following table :
Stop this crapola.
Take a look at the rwsem thing I pointed you to. After you understand
that, come back.
The WHOLE POINT of that thing was to use only 32-bit atomics on the hot
path. Don't even start think9ing about cmpxchg16b. If you cannot do your
atomics in 32-bit, they're broken.
Please. I realize that the rwsem implementation I did is subtle. But
really. Spend the time to understand it.
Linus
next prev parent reply other threads:[~2008-08-19 16:50 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-16 7:39 [PATCH] x86_64 : support atomic ops with 64 bits integer values Mathieu Desnoyers
2008-08-16 15:04 ` H. Peter Anvin
2008-08-16 15:43 ` Mathieu Desnoyers
2008-08-16 17:30 ` Linus Torvalds
2008-08-16 21:19 ` [RFC PATCH] Fair rwlock Mathieu Desnoyers
2008-08-16 21:33 ` Linus Torvalds
2008-08-17 7:53 ` [RFC PATCH] Fair low-latency rwlock v3 Mathieu Desnoyers
2008-08-17 16:17 ` Linus Torvalds
2008-08-17 19:10 ` [RFC PATCH] Fair low-latency rwlock v5 Mathieu Desnoyers
2008-08-17 21:30 ` [RFC PATCH] Fair low-latency rwlock v5 (updated benchmarks) Mathieu Desnoyers
2008-08-18 18:59 ` [RFC PATCH] Fair low-latency rwlock v5 Linus Torvalds
2008-08-18 23:25 ` Paul E. McKenney
2008-08-19 6:04 ` Mathieu Desnoyers
2008-08-19 7:33 ` Mathieu Desnoyers
2008-08-19 9:06 ` Mathieu Desnoyers
2008-08-19 16:48 ` Linus Torvalds [this message]
2008-08-21 20:50 ` [RFC PATCH] Writer-biased low-latency rwlock v8 Mathieu Desnoyers
2008-08-21 21:00 ` Linus Torvalds
2008-08-21 21:15 ` Linus Torvalds
2008-08-21 22:22 ` Linus Torvalds
2008-08-23 5:09 ` Mathieu Desnoyers
2008-08-23 18:02 ` Linus Torvalds
2008-08-23 20:30 ` Mathieu Desnoyers
2008-08-23 21:40 ` Linus Torvalds
2008-08-21 21:26 ` H. Peter Anvin
2008-08-21 21:41 ` Linus Torvalds
2008-08-25 19:20 ` [RFC PATCH] Fair low-latency rwlock v5 Peter Zijlstra
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