linux-kernel - Re: [PATCH v3] rwsem: Support optimistic spinning

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Message-ID: <CAGQ1y=4QvnR-uY+euqECYTJOwOXpxm2i1HBwUuwYEvYyVyArxQ@mail.gmail.com>
Date:	Thu, 1 May 2014 13:32:05 -0700
From:	Jason Low <jason.low2@...com>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Davidlohr Bueso <davidlohr@...com>, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E.McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] rwsem: Support optimistic spinning

On Thu, May 1, 2014 at 9:39 AM, Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> On Wed, 2014-04-30 at 20:21 -0700, Davidlohr Bueso wrote:
>
>> +
>> +static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
>> +{
>> +     struct task_struct *owner;
>> +     bool on_cpu = true;
>> +
>> +     if (need_resched())
>> +             return 0;
>> +
>> +     rcu_read_lock();
>> +     owner = ACCESS_ONCE(sem->owner);
>> +     if (owner)
>> +             on_cpu = owner->on_cpu;
>> +     rcu_read_unlock();
>> +
>> +     /*
>> +      * If lock->owner is not set, the mutex owner may have
>> +      * just acquired it and not set the owner yet or the mutex
>
> Nitpick. Change the above 2 mutex in comment to rwsem.

On that note, we may also change "lock->owner" to "sem->owner" for consistency.

Thanks,
Jason
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