From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <Waiman.Long@hp.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>
Subject: Re: [PATCH 1/7] locking/pvqspinlock: Only kick CPU at unlock time
Date: Tue, 14 Jul 2015 11:31:48 +0200 [thread overview]
Message-ID: <20150714093148.GY18673@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150713134828.GH3644@twins.programming.kicks-ass.net>
On Mon, Jul 13, 2015 at 03:48:28PM +0200, Peter Zijlstra wrote:
> @@ -239,9 +265,16 @@ static void pv_wait_head(struct qspinloc
> cpu_relax();
> }
>
> - WRITE_ONCE(pn->state, vcpu_halted);
> + /*
> + * Either pv_kick_node() advanced us and ->state is already
> + * vcpu_hashed and this store is superfluous, or this is the
> + * first in which case the below cmpxchg() provides the
> + * required barriers.
> + */
> + WRITE_ONCE(pn->state, vcpu_hashed);
The easier option is of course to just move this store into the branch
below. That immediately clarifies the logic and avoids the superfluous
store.
> if (!lp) { /* ONCE */
> lp = pv_hash(lock, pn);
> +
> /*
> * lp must be set before setting _Q_SLOW_VAL
> *
next prev parent reply other threads:[~2015-07-14 9:31 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-11 20:36 [PATCH 0/7] locking/qspinlock: Enhance pvqspinlock & introduce queued unfair lock Waiman Long
2015-07-11 20:36 ` [PATCH 1/7] locking/pvqspinlock: Only kick CPU at unlock time Waiman Long
2015-07-13 12:02 ` Peter Zijlstra
2015-07-13 12:31 ` Peter Zijlstra
2015-07-15 1:24 ` Waiman Long
2015-07-13 13:48 ` Peter Zijlstra
2015-07-14 9:31 ` Peter Zijlstra [this message]
2015-07-15 1:31 ` Waiman Long
2015-08-03 17:00 ` [tip:locking/core] " tip-bot for Waiman Long
2015-07-11 20:36 ` [PATCH 2/7] locking/pvqspinlock: Allow vCPUs kick-ahead Waiman Long
2015-07-13 13:52 ` Peter Zijlstra
2015-07-15 1:38 ` Waiman Long
2015-07-11 20:36 ` [PATCH 3/7] locking/pvqspinlock: Implement wait-early for overcommitted guest Waiman Long
2015-07-12 8:23 ` Peter Zijlstra
2015-07-13 19:50 ` Davidlohr Bueso
2015-07-15 1:39 ` Waiman Long
2015-07-11 20:36 ` [PATCH 4/7] locking/pvqspinlock: Collect slowpath lock statistics Waiman Long
2015-07-12 8:22 ` Peter Zijlstra
2015-07-14 18:48 ` Waiman Long
2015-07-11 20:36 ` [PATCH 5/7] locking/pvqspinlock: Add pending bit support Waiman Long
2015-07-12 8:21 ` Peter Zijlstra
2015-07-14 18:47 ` Waiman Long
2015-07-11 20:36 ` [PATCH 6/7] locking/qspinlock: A fairer queued unfair lock Waiman Long
2015-07-12 8:21 ` Peter Zijlstra
2015-07-14 18:47 ` Waiman Long
2015-07-14 20:45 ` Peter Zijlstra
2015-07-11 20:36 ` [PATCH 7/7] locking/qspinlock: Collect queued unfair lock slowpath statistics Waiman Long
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