linux-kernel - Re: [PATCH] locking/rwsem: reduce spinlock contention in wakeup after up_read/up

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Date:	Wed, 22 Apr 2015 16:19:23 -0400
From:	Waiman Long <waiman.long@...com>
To:	Jason Low <jason.low2@...com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH] locking/rwsem: reduce spinlock contention in wakeup after
 up_read/up_write

On 04/20/2015 04:23 PM, Jason Low wrote:
> On Fri, 2015-04-17 at 22:03 -0400, Waiman Long wrote:
>
>> diff --git a/include/linux/osq_lock.h b/include/linux/osq_lock.h
>> index 3a6490e..703ea5c 100644
>> --- a/include/linux/osq_lock.h
>> +++ b/include/linux/osq_lock.h
>> @@ -32,4 +32,9 @@ static inline void osq_lock_init(struct optimistic_spin_queue *lock)
>>   extern bool osq_lock(struct optimistic_spin_queue *lock);
>>   extern void osq_unlock(struct optimistic_spin_queue *lock);
>>
>> +static inline bool osq_is_locked(struct optimistic_spin_queue *lock)
>> +{
>> +	return atomic_read(&lock->tail) != OSQ_UNLOCKED_VAL;
>> +}
> Would it be better to separate the addition of osq_is_locked() into its
> own patch, since this can be useful for other situations and isn't just
> specific to the rwsem optimization.
>

I think the osq_lock.h change is too simple and straight forward to 
warrant a separate patch.

Cheers,
Longman
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