From: Peter Zijlstra <peterz@infradead.org>
To: Will Deacon <will.deacon@arm.com>
Cc: Waiman Long <longman@redhat.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, mingo@kernel.org,
boqun.feng@gmail.com, paulmck@linux.vnet.ibm.com,
catalin.marinas@arm.com
Subject: Re: [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath
Date: Thu, 20 Sep 2018 18:22:16 +0200 [thread overview]
Message-ID: <20180920162216.GR24142@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180920160832.GZ24124@hirez.programming.kicks-ass.net>
On Thu, Sep 20, 2018 at 06:08:32PM +0200, Peter Zijlstra wrote:
> Another approach might be to use something like:
>
> val = xchg_relaxed(&lock->locked_pending, _Q_PENDING_VAL | _Q_LOCKED_VAL);
> val |= atomic_read_acquire(&lock->val) & _Q_TAIL_MASK;
>
> combined with something like:
>
> /* 0,0,0 -> 0,1,1 - we won trylock */
> if (!(val & _Q_LOCKED_MASK)) {
That one doesn't actually work... let me think about this more.
> clear_pending(lock);
> return;
> }
>
> /* 0,0,1 -> 0,1,1 - we won pending */
> if (!(val & ~_Q_LOCKED_MASK)) {
> ...
> }
>
> /* *,0,1 -> *,1,1 - we won pending, but there's queueing */
> if (!(val & _Q_PENDING_VAL))
> clear_pending(lock);
>
> ...
>
>
> Hmmm?
next prev parent reply other threads:[~2018-09-20 16:22 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-05 16:58 [PATCH 00/10] kernel/locking: qspinlock improvements Will Deacon
2018-04-05 16:58 ` [PATCH 01/10] locking/qspinlock: Don't spin on pending->locked transition in slowpath Will Deacon
2018-04-05 16:58 ` [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Will Deacon
2018-04-05 17:07 ` Peter Zijlstra
2018-04-06 15:08 ` Will Deacon
2018-04-05 17:13 ` Peter Zijlstra
2018-04-05 21:16 ` Waiman Long
2018-04-06 15:08 ` Will Deacon
2018-04-06 20:50 ` Waiman Long
2018-04-06 21:09 ` Paul E. McKenney
2018-04-07 8:47 ` Peter Zijlstra
2018-04-07 23:37 ` Paul E. McKenney
2018-04-09 10:58 ` Will Deacon
2018-04-07 9:07 ` Peter Zijlstra
2018-04-09 10:58 ` Will Deacon
2018-04-09 14:54 ` Will Deacon
2018-04-09 15:54 ` Peter Zijlstra
2018-04-09 17:19 ` Will Deacon
2018-04-10 9:35 ` Peter Zijlstra
2018-09-20 16:08 ` Peter Zijlstra
2018-09-20 16:22 ` Peter Zijlstra [this message]
2018-04-09 19:33 ` Waiman Long
2018-04-09 17:55 ` Waiman Long
2018-04-10 13:49 ` Sasha Levin
2018-04-05 16:59 ` [PATCH 03/10] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue Will Deacon
2018-04-05 17:19 ` Peter Zijlstra
2018-04-06 10:54 ` Will Deacon
2018-04-05 16:59 ` [PATCH 04/10] locking/qspinlock: Use atomic_cond_read_acquire Will Deacon
2018-04-05 16:59 ` [PATCH 05/10] locking/mcs: Use smp_cond_load_acquire() in mcs spin loop Will Deacon
2018-04-05 16:59 ` [PATCH 06/10] barriers: Introduce smp_cond_load_relaxed and atomic_cond_read_relaxed Will Deacon
2018-04-05 17:22 ` Peter Zijlstra
2018-04-06 10:55 ` Will Deacon
2018-04-05 16:59 ` [PATCH 07/10] locking/qspinlock: Use smp_cond_load_relaxed to wait for next node Will Deacon
2018-04-05 16:59 ` [PATCH 08/10] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Will Deacon
2018-04-07 5:23 ` Boqun Feng
2018-04-05 16:59 ` [PATCH 09/10] locking/qspinlock: Make queued_spin_unlock use smp_store_release Will Deacon
2018-04-05 16:59 ` [PATCH 10/10] locking/qspinlock: Elide back-to-back RELEASE operations with smp_wmb() Will Deacon
2018-04-05 17:28 ` Peter Zijlstra
2018-04-06 11:34 ` Will Deacon
2018-04-06 13:05 ` Andrea Parri
2018-04-06 15:27 ` Will Deacon
2018-04-06 15:49 ` Andrea Parri
2018-04-07 5:47 ` Boqun Feng
2018-04-09 10:47 ` Will Deacon
2018-04-06 13:22 ` [PATCH 00/10] kernel/locking: qspinlock improvements Andrea Parri
2018-04-11 10:20 ` Catalin Marinas
2018-04-11 15:39 ` Andrea Parri
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