From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Andrew Morton <akpm@linux-foundation.org>,
Michel Lespinasse <walken@google.com>,
Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
George Spelvin <linux@horizon.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
Daniel J Blueman <daniel@numascale.com>,
Alexander Fyodorov <halcy@yandex.ru>,
Aswin Chandramouleeswaran <aswin@hp.com>,
Scott J Norton <scott.norton@hp.com>,
Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@hp.com>
Subject: Re: [PATCH v3 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation
Date: Fri, 31 Jan 2014 20:51:33 +0100 [thread overview]
Message-ID: <20140131195133.GP5002@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <52EBF871.5020603@hp.com>
On Fri, Jan 31, 2014 at 02:24:33PM -0500, Waiman Long wrote:
> On 01/31/2014 10:08 AM, Peter Zijlstra wrote:
> >Whereas for the straight cmpxchg() you'd get something relatively simple
> >like:
> >
> > mov %edx,%eax
> > lock cmpxchg %ecx,(%rbx)
> > cmp %edx,%eax
> > jne ...
>
> I believe the speeds of the lock functions are about the same. However,
> qspinlock has a much simpler unlock function which probably account of most
> of the speed gain.
The unlock path for ticket locks is a single "add[bw] $0x1,()", that should be
as fast as the single "movb 0,()" you have.
> >I suppose we could from the ticket code more and optimize the
> >uncontended path, but that'll make the contended path more expensive
> >again, although probably not as bad as hitting a new cacheline.
>
> I don't get what you are trying to say.
I said we could probably make the ticket lock function faster for the
uncontended case by making the contended case slightly more expensive.
next prev parent reply other threads:[~2014-01-31 19:51 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-28 18:19 [PATCH v3 0/2] qspinlock: Introducing a 4-byte queue spinlock Waiman Long
2014-01-28 18:19 ` [PATCH v3 1/2] qspinlock: Introducing a 4-byte queue spinlock implementation Waiman Long
2014-01-29 0:20 ` Andi Kleen
2014-01-29 0:20 ` Andi Kleen
2014-01-29 2:57 ` George Spelvin
2014-01-29 2:57 ` George Spelvin
2014-01-29 17:57 ` Waiman Long
2014-01-30 17:43 ` Rik van Riel
2014-01-30 19:00 ` Tim Chen
2014-01-30 19:28 ` Peter Zijlstra
2014-01-30 22:27 ` Tim Chen
2014-01-31 18:26 ` Waiman Long
2014-01-31 19:14 ` George Spelvin
2014-01-31 19:28 ` Waiman Long
2014-01-31 19:45 ` Peter Zijlstra
2014-01-31 18:16 ` Waiman Long
2014-01-30 19:35 ` Peter Zijlstra
2014-01-31 18:28 ` Waiman Long
2014-01-31 15:08 ` Peter Zijlstra
2014-01-31 19:24 ` Waiman Long
2014-01-31 19:51 ` Peter Zijlstra [this message]
2014-02-03 11:40 ` Peter Zijlstra
2014-02-06 3:10 ` Waiman Long
2014-02-07 18:17 ` Paul E. McKenney
2014-02-03 8:51 ` Raghavendra K T
2014-01-28 18:19 ` [PATCH v3 2/2] qspinlock, x86: Enable x86-64 to use queue spinlock Waiman Long
2014-01-30 17:45 ` Rik van Riel
2014-01-30 8:55 ` [PATCH v3 0/2] qspinlock: Introducing a 4-byte " Raghavendra K T
2014-01-30 15:38 ` Waiman Long
2014-01-30 18:49 ` Raghavendra K T
2014-02-03 8:51 ` Raghavendra K T
2014-02-06 3:09 ` Waiman Long
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