From: Waiman Long <waiman.long@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>,
Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH tip/locking/core v9 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt
Date: Mon, 09 Nov 2015 14:53:29 -0500 [thread overview]
Message-ID: <5640F9B9.7090306@hpe.com> (raw)
In-Reply-To: <20151109172945.GM17308@twins.programming.kicks-ass.net>
On 11/09/2015 12:29 PM, Peter Zijlstra wrote:
> On Fri, Nov 06, 2015 at 12:47:49PM -0500, Waiman Long wrote:
>> On 11/06/2015 09:50 AM, Peter Zijlstra wrote:
>>> *urgh*, last time we had:
>>>
>>> + if (pv_wait_head_or_steal())
>>> + goto stolen;
>>> while ((val = smp_load_acquire(&lock->val.counter))& _Q_LOCKED_PENDING_MASK)
>>> cpu_relax();
>>>
>>> ...
>>>
>>> +stolen:
>>> while (!(next = READ_ONCE(node->next)))
>>> cpu_relax();
>>>
>>> ...
>>>
>>> Now you completely overhaul the native code.. what happened?
>> I want to reuse as much of the existing native code as possible instead of
>> duplicating that in the PV function. The only difference now is that the PV
>> function will acquire that lock.
> Right; and while I doubt it hurts the native case (you did benchmark it
> I hope), I'm not too keen on the end result code wise.
>
> Maybe just keep the above.
I can jump over the smp_load_acquire() for PV instead of adding an
additional if block. For the native code, the only thing that was added
was an additional masking of val with _Q_TAIL_MASK which I don't think
will make too much of a difference.
>
>> Semantically, I don't want to call the lock
>> acquisition as lock stealing as the queue head is entitled to get the lock
>> next.
> Fair enough I suppose, pv_wait_head_or_lock() then?
>
I am fine with that name.
>> I can rename pv_queued_spin_trylock_unfair() to
>> pv_queued_spin_steal_lock() to emphasize the fact that this is the routine
>> where lock stealing happens.
> OK.
>
Cheers,
Longman
next prev parent reply other threads:[~2015-11-09 19:53 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-30 23:26 [PATCH tip/locking/core v9 0/6] locking/qspinlock: Enhance pvqspinlock Waiman Long
2015-10-30 23:26 ` [PATCH tip/locking/core v9 1/6] locking/qspinlock: Use _acquire/_release versions of cmpxchg & xchg Waiman Long
2015-10-30 23:26 ` [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Waiman Long
2015-11-02 16:36 ` Peter Zijlstra
2015-11-02 22:54 ` Peter Zijlstra
2015-11-05 16:42 ` Waiman Long
2015-11-05 16:49 ` Peter Zijlstra
2015-11-05 16:06 ` Waiman Long
2015-11-05 16:39 ` Peter Zijlstra
2015-11-05 16:52 ` Waiman Long
2015-10-30 23:26 ` [PATCH tip/locking/core v9 3/6] locking/pvqspinlock, x86: Optimize PV unlock code path Waiman Long
2015-10-30 23:26 ` [PATCH tip/locking/core v9 4/6] locking/pvqspinlock: Collect slowpath lock statistics Waiman Long
2015-11-02 16:40 ` Peter Zijlstra
2015-11-05 16:29 ` Waiman Long
2015-11-05 16:43 ` Peter Zijlstra
2015-11-05 16:59 ` Waiman Long
2015-11-05 17:09 ` Peter Zijlstra
2015-11-05 17:34 ` Waiman Long
2015-10-30 23:26 ` [PATCH tip/locking/core v9 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long
2015-11-06 14:50 ` Peter Zijlstra
2015-11-06 17:47 ` Waiman Long
2015-11-09 17:29 ` Peter Zijlstra
2015-11-09 19:53 ` Waiman Long [this message]
2015-10-30 23:26 ` [PATCH tip/locking/core v9 6/6] locking/pvqspinlock: Queue node adaptive spinning Waiman Long
2015-11-06 15:01 ` Peter Zijlstra
2015-11-06 17:54 ` Waiman Long
2015-11-06 20:37 ` Peter Zijlstra
2015-11-09 16:51 ` Waiman Long
2015-11-09 17:33 ` Peter Zijlstra
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