From: Waiman Long <waiman.long@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ding Tianhong <dingtianhong@huawei.com>,
Jason Low <jason.low2@hpe.com>,
Davidlohr Bueso <dave@stgolabs.net>,
"Paul E. McKenney" <paulmck@us.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <Will.Deacon@arm.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
Waiman Long <Waiman.Long@hp.com>
Subject: Re: [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin()
Date: Mon, 15 Feb 2016 17:06:52 -0500 [thread overview]
Message-ID: <56C24BFC.4080908@hpe.com> (raw)
In-Reply-To: <20160212202355.GY6357@twins.programming.kicks-ass.net>
On 02/12/2016 03:23 PM, Peter Zijlstra wrote:
> On Fri, Feb 12, 2016 at 12:32:12PM -0500, Waiman Long wrote:
>> This patch adds a new waiter parameter to the mutex_optimistic_spin()
>> function to prepare it to be used by a waiter-spinner that doesn't
>> need to go into the OSQ as there can only be one waiter-spinner which
>> is the head of the waiting queue.
> Does not explain why..
>
>> static bool mutex_optimistic_spin(struct mutex *lock,
>> + struct ww_acquire_ctx *ww_ctx,
>> + const bool use_ww_ctx, int waiter)
>> {
>> struct task_struct *task = current;
>> + bool acquired = false;
>>
>> + if (!waiter) {
>> + if (!mutex_can_spin_on_owner(lock))
>> + goto done;
> Why doesn't the waiter have to check mutex_can_spin_on_owner() ?
The reason why regular spinner need to call mutex_can_spin_on_owner is
because we want to avoid the overhead of the OSQ if we can't spin. As
mutex_can_spin_on_owner() is similar to mutex_spin_on_owner(), the
waiter-spinner will exit spinning after calling mutex_spin_on_owner().
Cheers,
Longman
next prev parent reply other threads:[~2016-02-15 22:07 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-12 17:32 [PATCH v2 0/4] locking/mutex: Enable optimistic spinning of lock waiter Waiman Long
2016-02-12 17:32 ` [PATCH v2 1/4] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long
2016-02-12 20:23 ` Peter Zijlstra
2016-02-12 22:14 ` Davidlohr Bueso
2016-02-13 12:10 ` Peter Zijlstra
2016-02-13 18:14 ` Davidlohr Bueso
2016-02-16 2:15 ` Jason Low
2016-02-16 2:22 ` Jason Low
2016-02-16 8:53 ` Peter Zijlstra
2016-02-17 1:40 ` Waiman Long
2016-02-15 22:06 ` Waiman Long [this message]
2016-02-12 20:40 ` Peter Zijlstra
2016-02-15 23:55 ` Waiman Long
2016-02-16 3:00 ` Jason Low
2016-02-16 3:30 ` Waiman Long
2016-02-12 22:02 ` Davidlohr Bueso
2016-02-12 22:09 ` Davidlohr Bueso
2016-02-16 0:03 ` Waiman Long
2016-02-12 17:32 ` [PATCH v2 2/4] locking/mutex: Enable optimistic spinning of woken task in wait queue Waiman Long
2016-02-12 17:32 ` [PATCH v2 3/4] locking/mutex: Avoid missed wakeup of mutex waiter Waiman Long
2016-02-12 17:32 ` [PATCH v2 4/4] sched/fair: Abort wakeup when task is no longer in a sleeping state Waiman Long
2016-02-12 20:18 ` Peter Zijlstra
2016-02-12 21:22 ` Waiman Long
2016-02-13 12:09 ` Peter Zijlstra
2016-02-16 8:51 ` [PATCH v2 0/4] locking/mutex: Enable optimistic spinning of lock waiter Peter Zijlstra
2016-02-17 1:39 ` Waiman Long
2016-03-22 3:19 ` Waiman Long
2016-03-22 9:59 ` Peter Zijlstra
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