From: Waiman Long <longman@redhat.com>
To: Will Deacon <will.deacon@arm.com>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, peterz@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: Mon, 9 Apr 2018 15:33:21 -0400 [thread overview]
Message-ID: <5e7211d4-43f0-297e-dbbc-8e87721f96b8@redhat.com> (raw)
In-Reply-To: <20180409145409.GA9661@arm.com>
On 04/09/2018 10:54 AM, Will Deacon wrote:
>
>>> I am not against this patch, but we certainly need to find out a way to
>>> bring the performance number up closer to what it is before applying
>>> the patch.
>> We certainly need to *understand* where the drop is coming from, because
>> the two-threaded case is still just a CAS on x86 with and without this
>> patch series. Generally, there's a throughput cost when ensuring fairness
>> and forward-progress otherwise we'd all be using test-and-set.
> Whilst I think we still need to address my questions above, I've had a
> crack at the diff below. Please can you give it a spin? It sticks a trylock
> on the slowpath before setting pending and replaces the CAS-based set
> with an xchg (which I *think* is safe, but will need to ponder it some
> more).
>
> Thanks,
>
> Will
>
Unfortunately, this patch didn't help.
pending count = 777
queuing count = 9,991,272
locking rate = 4,087 kop/s
-Longman
WARNING: multiple messages have this Message-ID (diff)
From: longman@redhat.com (Waiman Long)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath
Date: Mon, 9 Apr 2018 15:33:21 -0400 [thread overview]
Message-ID: <5e7211d4-43f0-297e-dbbc-8e87721f96b8@redhat.com> (raw)
In-Reply-To: <20180409145409.GA9661@arm.com>
On 04/09/2018 10:54 AM, Will Deacon wrote:
>
>>> I am not against this patch, but we certainly need to find out a way to
>>> bring the performance number up closer to what it is before applying
>>> the patch.
>> We certainly need to *understand* where the drop is coming from, because
>> the two-threaded case is still just a CAS on x86 with and without this
>> patch series. Generally, there's a throughput cost when ensuring fairness
>> and forward-progress otherwise we'd all be using test-and-set.
> Whilst I think we still need to address my questions above, I've had a
> crack at the diff below. Please can you give it a spin? It sticks a trylock
> on the slowpath before setting pending and replaces the CAS-based set
> with an xchg (which I *think* is safe, but will need to ponder it some
> more).
>
> Thanks,
>
> Will
>
Unfortunately, this patch didn't help.
pending count = 777
queuing count = 9,991,272
locking rate = 4,087 kop/s
-Longman
next prev parent reply other threads:[~2018-04-09 19:33 UTC|newest]
Thread overview: 94+ 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 ` 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 ` Will Deacon
2018-04-05 16:58 ` [PATCH 02/10] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Will Deacon
2018-04-05 16:58 ` Will Deacon
2018-04-05 17:07 ` Peter Zijlstra
2018-04-05 17:07 ` Peter Zijlstra
2018-04-06 15:08 ` Will Deacon
2018-04-06 15:08 ` Will Deacon
2018-04-05 17:13 ` Peter Zijlstra
2018-04-05 17:13 ` Peter Zijlstra
2018-04-05 21:16 ` Waiman Long
2018-04-05 21:16 ` Waiman Long
2018-04-06 15:08 ` Will Deacon
2018-04-06 15:08 ` Will Deacon
2018-04-06 20:50 ` Waiman Long
2018-04-06 20:50 ` Waiman Long
2018-04-06 21:09 ` Paul E. McKenney
2018-04-06 21:09 ` Paul E. McKenney
2018-04-07 8:47 ` Peter Zijlstra
2018-04-07 8:47 ` Peter Zijlstra
2018-04-07 23:37 ` Paul E. McKenney
2018-04-07 23:37 ` Paul E. McKenney
2018-04-09 10:58 ` Will Deacon
2018-04-09 10:58 ` Will Deacon
2018-04-07 9:07 ` Peter Zijlstra
2018-04-07 9:07 ` Peter Zijlstra
2018-04-09 10:58 ` Will Deacon
2018-04-09 10:58 ` Will Deacon
2018-04-09 14:54 ` Will Deacon
2018-04-09 14:54 ` Will Deacon
2018-04-09 15:54 ` Peter Zijlstra
2018-04-09 15:54 ` Peter Zijlstra
2018-04-09 17:19 ` Will Deacon
2018-04-09 17:19 ` Will Deacon
2018-04-10 9:35 ` Peter Zijlstra
2018-04-10 9:35 ` Peter Zijlstra
2018-09-20 16:08 ` Peter Zijlstra
2018-09-20 16:08 ` Peter Zijlstra
2018-09-20 16:22 ` Peter Zijlstra
2018-09-20 16:22 ` Peter Zijlstra
2018-04-09 19:33 ` Waiman Long [this message]
2018-04-09 19:33 ` Waiman Long
2018-04-09 17:55 ` Waiman Long
2018-04-09 17:55 ` Waiman Long
2018-04-10 13:49 ` Sasha Levin
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 16:59 ` Will Deacon
2018-04-05 17:19 ` Peter Zijlstra
2018-04-05 17:19 ` Peter Zijlstra
2018-04-06 10:54 ` Will Deacon
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 ` 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 ` 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 16:59 ` Will Deacon
2018-04-05 17:22 ` Peter Zijlstra
2018-04-05 17:22 ` Peter Zijlstra
2018-04-06 10:55 ` Will Deacon
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 ` Will Deacon
2018-04-05 16:59 ` [PATCH 08/10] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Will Deacon
2018-04-05 16:59 ` Will Deacon
2018-04-07 5:23 ` Boqun Feng
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 ` 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 16:59 ` Will Deacon
2018-04-05 17:28 ` Peter Zijlstra
2018-04-05 17:28 ` Peter Zijlstra
2018-04-06 11:34 ` Will Deacon
2018-04-06 11:34 ` Will Deacon
2018-04-06 13:05 ` Andrea Parri
2018-04-06 13:05 ` Andrea Parri
2018-04-06 15:27 ` Will Deacon
2018-04-06 15:27 ` Will Deacon
2018-04-06 15:49 ` Andrea Parri
2018-04-06 15:49 ` Andrea Parri
2018-04-07 5:47 ` Boqun Feng
2018-04-07 5:47 ` Boqun Feng
2018-04-09 10:47 ` Will Deacon
2018-04-09 10:47 ` Will Deacon
2018-04-06 13:22 ` [PATCH 00/10] kernel/locking: qspinlock improvements Andrea Parri
2018-04-06 13:22 ` Andrea Parri
2018-04-11 10:20 ` Catalin Marinas
2018-04-11 10:20 ` Catalin Marinas
2018-04-11 15:39 ` Andrea Parri
2018-04-11 15:39 ` Andrea Parri
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