From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH] locking/rwsem: Remove arch specific rwsem files Date: Mon, 11 Feb 2019 11:57:29 +0100 Message-ID: <20190211105729.GH32534@hirez.programming.kicks-ass.net> References: <1549850450-10171-1-git-send-email-longman@redhat.com> <20190211093601.GT32511@hirez.programming.kicks-ass.net> <20190211094044.GG32534@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=ncSqt2PLo4pdd6rz79XO7avg043G84xdBBaEBPJMQio=; b=qDm2nKYqx9z8YF tIYUUJ9bM4gwp9w5NmH423XCwlcxiRSB3+frUDOe1sU5kVsY6HSFiaR1fgTriv8En/7lOMtjLnZ/c ibg2RiROJDcahPpg9Oa9B+D+5eoX0zerynE8CiKSDu0nwfbCln8TG2TB2h4no47yJ/KJrzb1Dq2tt mXJTF+uAGLrPj2lsHKO4Tznn9Y1tLSxSswQ1rQQ/Z28AeTQ5NsWvz3QJKtveI/uxxSSZzleG6XuNp UTdYAF1IaZ7JmweLCSxa8hlZqTgHOfWEH59MXUanJwmGZNnZ+FQ98n6pZgmTXgZ+AssyQow2KfXVf 6317SD9ZMSltkbP81duQ==; DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=H4FKzYfPZLq064fpvMaxRyPbo6mwWdcW0fXgF0VWycY=; b=0U7b+TSCrog3RuwY+5aIN+sYF hv/X24vYbiLjaTad2ObIWMdW7Cp2r/5OoaUpAoXctxc/VYvLlvd8Jg876MzN8pgTjMW8CZ3P1r/K0 V/l2fLFDfV1pgkRUFU9xzkmvMbliuyWhgYyM+5CQxhzMD875i3oOU3bLFnwzd6Z1n69EGanR7kB8K jwNrR1x25pUNYuM1WWMfiO/CFWtHodA2Mmztx2gmUubEivvDlwHAS5qsyCdKdk3uPgvtfWI5OmsKO 4D+eGwN6yN1S/MmNn/tvUdF/HvrjMc60lzn96bluUcUP+BS/cOvXQ1En41wBhdBg2BY4eZU6c4md3 EkSdmP65w==; Content-Disposition: inline In-Reply-To: <20190211094044.GG32534@hirez.programming.kicks-ass.net> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Waiman Long Cc: linux-arch@vger.kernel.org, linux-xtensa@linux-xtensa.org, Davidlohr Bueso , linux-ia64@vger.kernel.org, Tim Chen , Arnd Bergmann , linux-sh@vger.kernel.org, linux-hexagon@vger.kernel.org, x86@kernel.org, Will Deacon , linux-kernel@vger.kernel.org, Linus Torvalds , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , linux-alpha@vger.kernel.org, sparclinux@vger.kernel.org, Thomas Gleixner , linuxppc-dev@lists.ozlabs.org, Andrew Morton , linux-arm-kernel@lists.infradead.org On Mon, Feb 11, 2019 at 10:40:44AM +0100, Peter Zijlstra wrote: > 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 ? Ah, I see they already used asm-generic/rwsem.h which has similar code to the above.