From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: linux-arch@vger.kernel.org, linux-xtensa@linux-xtensa.org,
Davidlohr Bueso <dave@stgolabs.net>,
linux-ia64@vger.kernel.org, Tim Chen <tim.c.chen@linux.intel.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-sh@vger.kernel.org, linux-hexagon@vger.kernel.org,
x86@kernel.org, Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H. Peter Anvin" <hpa@zytor.com>,
linux-alpha@vger.kernel.org, sparclinux@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
linuxppc-dev@lists.ozlabs.org,
Andrew Morton <akpm@linux-foundation.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] locking/rwsem: Remove arch specific rwsem files
Date: Mon, 11 Feb 2019 10:40:44 +0100 [thread overview]
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 ?
next prev parent reply other threads:[~2019-02-11 9:42 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-11 2:00 [PATCH] locking/rwsem: Remove arch specific rwsem files 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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