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>,
Imre Deak <imre.deak@intel.com>
Subject: Re: [PATCH v4 2/3] locking/mutex: Enable optimistic spinning of woken task in wait queue
Date: Tue, 9 Aug 2016 13:49:01 -0400 [thread overview]
Message-ID: <57AA178D.2050604@hpe.com> (raw)
In-Reply-To: <20160808172938.GY6862@twins.programming.kicks-ass.net>
On 08/08/2016 01:29 PM, Peter Zijlstra wrote:
> On Mon, Jul 18, 2016 at 04:39:25PM -0400, Waiman Long wrote:
>> Ding Tianhong reported a live-lock situation where a constant stream
>> of incoming optimistic spinners blocked a task in the wait list from
>> getting the mutex.
>>
>> This patch attempts to fix this live-lock condition by enabling the
>> woken task in the wait queue to enter into an optimistic spinning
>> loop itself in parallel with the regular spinners in the OSQ. This
>> should prevent the live-lock condition from happening.
> No, two spinners are not in fact starvation proof. It makes the reported
> life-lock scenario much less likely, but it does not guarantee anything.
Yes, I should have said reducing the chance of live-locking.
>> + /*
>> + * Optimistically spinning on the mutex without the wait lock
> There should either be a '.' at the end of that line, or the next line
> should not start with a capital.
>
> Also, I don't see how the two sentences are related, should they be in
> the same paragraph?
Sorry for the missing '.', and I will split it into 2 paragraphs.
Cheers,
Longman
next prev parent reply other threads:[~2016-08-09 17:49 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-18 20:39 [PATCH v4 0/3] locking/mutex: Enable optimistic spinning of lock waiter Waiman Long
2016-07-18 20:39 ` [PATCH v4 1/3] locking/mutex: Add waiter parameter to mutex_optimistic_spin() Waiman Long
2016-08-08 17:26 ` Peter Zijlstra
2016-08-09 17:36 ` Waiman Long
2016-07-18 20:39 ` [PATCH v4 2/3] locking/mutex: Enable optimistic spinning of woken task in wait queue Waiman Long
2016-08-08 17:29 ` Peter Zijlstra
2016-08-09 17:49 ` Waiman Long [this message]
2016-07-18 20:39 ` [PATCH v4 3/3] locking/mutex: Ensure forward progress of waiter-spinner Waiman Long
2016-08-08 17:37 ` Peter Zijlstra
2016-08-09 18:00 ` Waiman Long
2016-08-10 9:29 ` Peter Zijlstra
2016-08-10 17:51 ` Waiman Long
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