linux-kernel - Re: [PATCH v8 14/19] locking/rwsem: Enable time-based spinning on reader-owned rwsem

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Date:   Tue, 4 Jun 2019 12:54:39 -0400
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH v8 14/19] locking/rwsem: Enable time-based spinning on
 reader-owned rwsem

On 6/4/19 5:03 AM, Peter Zijlstra wrote:
> On Mon, May 20, 2019 at 04:59:13PM -0400, Waiman Long wrote:
>> +static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
>> +{
>> +	long owner = atomic_long_read(&sem->owner);
>> +
>> +	while (owner & RWSEM_READER_OWNED) {
>> +		if (owner & RWSEM_NONSPINNABLE)
>> +			break;
>> +		owner = atomic_long_cmpxchg(&sem->owner, owner,
>> +					    owner | RWSEM_NONSPINNABLE);
>> +	}
>> +}
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -206,12 +206,13 @@ static inline void rwsem_set_nonspinnabl
>  {
>  	long owner = atomic_long_read(&sem->owner);
>  
> -	while (owner & RWSEM_READER_OWNED) {
> +	do {
> +		if (!(owner & RWSEM_READER_OWNED))
> +			break;
>  		if (owner & RWSEM_NONSPINNABLE)
>  			break;
> -		owner = atomic_long_cmpxchg(&sem->owner, owner,
> -					    owner | RWSEM_NONSPINNABLE);
> -	}
> +	} while (!atomic_long_try_cmpxchg(&sem->owner, &owner,
> +					  owner | RWSEM_NONSPINNABLE));
>  }
>  
>  /*

Sure.

Thanks,
Longman