From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <Waiman.Long@hpe.com>
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@hp.com>,
Douglas Hatch <doug.hatch@hp.com>,
Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt
Date: Mon, 14 Sep 2015 16:04:56 +0200 [thread overview]
Message-ID: <20150914140456.GU18489@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1441996658-62854-6-git-send-email-Waiman.Long@hpe.com>
On Fri, Sep 11, 2015 at 02:37:37PM -0400, Waiman Long wrote:
> This patch allows one attempt for the lock waiter to steal the lock
> when entering the PV slowpath. This helps to reduce the performance
> penalty caused by lock waiter preemption while not having much of
> the downsides of a real unfair lock.
> @@ -416,7 +414,8 @@ queue:
> * does not imply a full barrier.
> *
> */
If it really were once, like the Changelog says it is, then you could
have simply added:
if (pv_try_steal_lock(...))
goto release;
here, and not wrecked pv_wait_head() like you did. Note that if you do
it like this, you also do not need to play games with the hash, because
you'll never get into that situation.
> - pv_wait_head(lock, node);
> + if (pv_wait_head_and_lock(lock, node, tail))
> + goto release;
> while ((val = smp_load_acquire(&lock->val.counter)) & _Q_LOCKED_PENDING_MASK)
> cpu_relax();
>
next prev parent reply other threads:[~2015-09-14 14:05 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-11 18:37 [PATCH v6 0/6] locking/qspinlock: Enhance pvqspinlock performance Waiman Long
2015-09-11 18:37 ` [PATCH v6 1/6] locking/qspinlock: relaxes cmpxchg & xchg ops in native code Waiman Long
2015-09-11 22:27 ` Davidlohr Bueso
2015-09-14 12:06 ` Peter Zijlstra
2015-09-14 18:40 ` Waiman Long
2015-09-14 15:16 ` Waiman Long
2015-09-11 18:37 ` [PATCH v6 2/6] locking/pvqspinlock: Unconditional PV kick with _Q_SLOW_VAL Waiman Long
2015-09-18 8:50 ` [tip:locking/core] locking/pvqspinlock: Kick the PV CPU unconditionally when _Q_SLOW_VAL tip-bot for Waiman Long
2015-09-11 18:37 ` [PATCH v6 3/6] locking/pvqspinlock, x86: Optimize PV unlock code path Waiman Long
2015-09-11 18:37 ` [PATCH v6 4/6] locking/pvqspinlock: Collect slowpath lock statistics Waiman Long
2015-09-11 23:13 ` Davidlohr Bueso
2015-09-14 15:25 ` Waiman Long
2015-09-14 21:41 ` Davidlohr Bueso
2015-09-15 3:47 ` Waiman Long
2015-09-11 18:37 ` [PATCH v6 5/6] locking/pvqspinlock: Allow 1 lock stealing attempt Waiman Long
2015-09-14 13:57 ` Peter Zijlstra
2015-09-14 19:02 ` Waiman Long
2015-09-14 14:00 ` Peter Zijlstra
2015-09-14 19:15 ` Waiman Long
2015-09-14 19:38 ` Waiman Long
2015-09-15 8:24 ` Peter Zijlstra
2015-09-15 15:29 ` Waiman Long
2015-09-16 15:01 ` Peter Zijlstra
2015-09-17 15:08 ` Waiman Long
2015-09-14 14:04 ` Peter Zijlstra [this message]
2015-09-14 19:19 ` Waiman Long
2015-09-11 18:37 ` [PATCH v6 6/6] locking/pvqspinlock: Queue node adaptive spinning Waiman Long
2015-09-14 14:10 ` Peter Zijlstra
2015-09-14 19:37 ` Waiman Long
2015-09-15 8:38 ` Peter Zijlstra
2015-09-15 15:32 ` Waiman Long
2015-09-16 15:03 ` Peter Zijlstra
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