From: Peter Zijlstra <peterz@infradead.org>
To: George Spelvin <linux@horizon.com>
Cc: Waiman.Long@hp.com, akpm@linux-foundation.org,
andi@firstfloor.org, arnd@arndb.de, aswin@hp.com, hpa@zytor.com,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
mingo@redhat.com, paulmck@linux.vnet.ibm.com,
raghavendra.kt@linux.vnet.ibm.com, riel@redhat.com,
rostedt@goodmis.org, scott.norton@hp.com, tglx@linutronix.de,
tim.c.chen@linux.intel.com, torvalds@linux-foundation.org,
walken@google.com, x86@kernel.org
Subject: Re: [PATCH v11 0/4] Introducing a queue read/write lock implementation
Date: Fri, 31 Jan 2014 11:17:29 +0100 [thread overview]
Message-ID: <20140131101729.GA8874@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20140131100348.8867.qmail@science.horizon.com>
On Fri, Jan 31, 2014 at 05:03:48AM -0500, George Spelvin wrote:
> How about getting rid of that TICKET_MSB mess and doing something like:
>
> #define TICKET_MASK 0xFFFF
>
> static inline void ticket_spin_unlock(atomic_t *tickets)
> {
> u32 t = *tickets;
>
> smp_mb__before_atomic_inc();
>
> /* Increment the low 16 bits without affecting the upper. */
> if (unlikely((~t & TICKET_MASK) == 0))
> atomic_add(-(atomic_t)TICKET_MASK, tickets);
> else
> atomic_inc(tickets);
> }
>
> That also allows up to 2^16 waiters, up from 2^15.
> (Minus one on both cases, if you want to be fussy.)
Ah indeed. That'll work. That said, any arch that can single-copy
address shorts can probably do better than this generic atomic_t thing.
My main point was that we should seriously look at a ticket lock instead
of the MCS one, because while the MCS has better contention behaviour,
we shouldn't optimize locks for the worst contention.
next prev parent reply other threads:[~2014-01-31 10:17 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-24 4:28 [PATCH v11 0/4] Introducing a queue read/write lock implementation Waiman Long
2014-01-24 4:28 ` [PATCH v11 1/4] qrwlock: A " Waiman Long
2014-01-24 8:25 ` Peter Zijlstra
2014-01-25 4:39 ` Waiman Long
2014-01-24 4:28 ` [PATCH v11 2/4] qrwlock, x86: Enable x86 to use queue read/write lock Waiman Long
2014-01-24 4:28 ` [PATCH v11 3/4] qrwlock, x86: Add char and short as atomic data type in x86 Waiman Long
2014-01-24 4:28 ` [PATCH v11 4/4] qrwlock: Use the mcs_spinlock helper functions for MCS queuing Waiman Long
2014-01-24 8:26 ` Peter Zijlstra
2014-01-25 4:30 ` Waiman Long
2014-01-30 13:04 ` [PATCH v11 0/4] Introducing a queue read/write lock implementation Peter Zijlstra
2014-01-30 15:17 ` Peter Zijlstra
2014-01-30 15:43 ` Waiman Long
2014-01-30 15:50 ` Waiman Long
2014-01-30 15:53 ` Peter Zijlstra
2014-01-30 15:44 ` Peter Zijlstra
2014-01-30 17:52 ` Will Deacon
2014-01-30 18:05 ` Peter Zijlstra
2014-01-30 18:11 ` Will Deacon
2014-01-30 18:16 ` Peter Zijlstra
2014-01-31 9:26 ` Peter Zijlstra
2014-01-31 10:03 ` George Spelvin
2014-01-31 10:17 ` Peter Zijlstra [this message]
2014-01-31 11:30 ` Peter Zijlstra
2014-02-01 23:22 ` Paul E. McKenney
2014-01-31 18:59 ` Waiman Long
2014-01-31 19:47 ` Peter Zijlstra
2014-02-01 10:38 ` George Spelvin
2014-01-31 20:14 ` Peter Zijlstra
2014-01-31 21:09 ` Waiman Long
2014-02-01 1:29 ` Davidlohr Bueso
2014-02-02 9:03 ` Ingo Molnar
2014-02-03 11:38 ` Peter Zijlstra
2014-02-06 3:08 ` Waiman Long
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