From: Davidlohr Bueso <dave@stgolabs.net>
To: Waiman Long <waiman.long@hpe.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-s390@vger.kernel.org, linux-arch@vger.kernel.org,
Jason Low <jason.low2@hp.com>, Dave Chinner <david@fromorbit.com>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier
Date: Fri, 17 Jun 2016 09:46:59 -0700 [thread overview]
Message-ID: <20160617164659.GC14591@linux-80c1.suse> (raw)
In-Reply-To: <20160617162926.GB14591@linux-80c1.suse>
On Fri, 17 Jun 2016, Davidlohr Bueso wrote:
>On Fri, 17 Jun 2016, Waiman Long wrote:
>
>>On 06/16/2016 09:11 PM, Davidlohr Bueso wrote:
>>>On Wed, 15 Jun 2016, Peter Zijlstra wrote:
>>>
>>>>Yeah, see a few patches further in this series, where he guards a
>>>>variables with the osq_lock.
>>>
>>>So one problem I have with all this is that if we are hardening
>>>osq_lock/unlock()
>>>because of some future use that is specific to rwsems, then we
>>>will immediately
>>>be hurting mutexes for no good reason.
>>>
>>
>>I am going to change it to use smp_acquire__after_ctrl_dep() as
>>suggested by PeterZ. Is that a good enough compromise? I have also
>>changed the xchg in the unlock side to xchg_release which could help
>>performance in some archs. The thing is when developers see the name
>>osq_lock/osq_unlock, they will naturally assume the proper barrriers
>>are provided which is not currently the case.
>
>Oh, from your discussions with Boqun, I was under the impression that ->locked
>was now going to be properly ordered in all cases now, which is why
>I worry about mutexes.
>
>>Anyway, the change won't affect x86, it is probably ARM or PPC that
>>may have an impact.
>
>Yes, that xchg() won't affect x86, but adding an smp_store_release(node->locked, 1)
>or such will obviously.
nm this last part, you're right, x86 smp_store_release is a nop.
next prev parent reply other threads:[~2016-06-17 16:47 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-14 22:48 [RFC PATCH-tip v2 0/6] locking/rwsem: Enable reader optimistic spinning Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier Waiman Long
2016-06-15 8:04 ` Boqun Feng
2016-06-15 17:18 ` Peter Zijlstra
2016-06-15 19:01 ` Waiman Long
2016-06-16 2:19 ` Boqun Feng
2016-06-16 10:16 ` Will Deacon
2016-06-16 21:35 ` Waiman Long
2016-06-17 0:48 ` Boqun Feng
2016-06-17 15:26 ` Waiman Long
2016-06-17 15:45 ` Will Deacon
2016-06-17 18:17 ` Waiman Long
2016-06-18 8:46 ` Boqun Feng
2016-06-20 7:59 ` Will Deacon
2016-06-15 16:56 ` Davidlohr Bueso
2016-06-15 17:12 ` Peter Zijlstra
2016-06-15 18:27 ` Davidlohr Bueso
2016-06-15 18:40 ` Peter Zijlstra
2016-06-15 18:56 ` Davidlohr Bueso
2016-06-17 1:11 ` Davidlohr Bueso
2016-06-17 14:28 ` Waiman Long
2016-06-17 16:29 ` Davidlohr Bueso
2016-06-17 16:46 ` Davidlohr Bueso [this message]
2016-06-15 19:08 ` Waiman Long
2016-06-15 20:04 ` Waiman Long
2016-06-15 21:59 ` Peter Zijlstra
2016-06-14 22:48 ` [RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP Waiman Long
2016-06-15 17:22 ` Peter Zijlstra
2016-06-15 19:17 ` Waiman Long
2016-06-16 2:14 ` Davidlohr Bueso
2016-06-16 21:25 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 3/6] locking/rwsem: Enable count-based spinning on reader Waiman Long
2016-06-15 17:38 ` Peter Zijlstra
2016-06-15 19:28 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 4/6] locking/rwsem: move down rwsem_down_read_failed function Waiman Long
2016-06-15 17:40 ` Peter Zijlstra
2016-06-15 19:21 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 5/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation Waiman Long
2016-06-15 17:43 ` Peter Zijlstra
2016-06-15 19:31 ` Waiman Long
2016-06-15 21:57 ` Peter Zijlstra
2016-06-15 17:45 ` Peter Zijlstra
2016-06-15 19:35 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 6/6] locking/rwsem: Enable spinning readers Waiman Long
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