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From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org,
	sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org,
	linux-arch@vger.kernel.org, x86@kernel.org,
	Arnd Bergmann <arnd@arndb.de>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Tim Chen <tim.c.chen@linux.intel.com>
Subject: Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
Date: Mon, 11 Feb 2019 10:40:44 +0100
Message-ID: <20190211094044.GG32534@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190211093601.GT32511@hirez.programming.kicks-ass.net>

On Mon, Feb 11, 2019 at 10:36:01AM +0100, Peter Zijlstra wrote:
> On Sun, Feb 10, 2019 at 09:00:50PM -0500, Waiman Long wrote:
> > +static inline int __down_read_trylock(struct rw_semaphore *sem)
> > +{
> > +	long tmp;
> > +
> > +	while ((tmp = atomic_long_read(&sem->count)) >= 0) {
> > +		if (tmp == atomic_long_cmpxchg_acquire(&sem->count, tmp,
> > +				   tmp + RWSEM_ACTIVE_READ_BIAS)) {
> > +			return 1;
> 
> That really wants to be:
> 
> 		if (atomic_long_try_cmpxchg_acquire(&sem->count, &tmp,
> 						    tmp + RWSEM_ACTIVE_READ_BIAS))
> 
> > +		}
> > +	}
> > +	return 0;
> > +}

Also, the is the one case where LL/SC can actually do 'better'. Do you
have benchmarks for say PowerPC or ARM64 ?

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-11  2:00 Waiman Long
2019-02-11  2:08 ` Waiman Long
2019-02-11  7:11   ` Ingo Molnar
2019-02-11 10:39     ` Ingo Molnar
2019-02-11 10:52       ` Will Deacon
2019-02-11 10:55         ` Ingo Molnar
2019-02-11 13:32       ` Waiman Long
2019-02-11  9:36 ` Peter Zijlstra
2019-02-11  9:40   ` Peter Zijlstra [this message]
2019-02-11 10:57     ` Peter Zijlstra
2019-02-11 11:58 ` Peter Zijlstra
2019-02-11 16:35   ` Waiman Long
2019-02-11 17:04     ` Peter Zijlstra

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