From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Date: Wed, 27 Jan 2016 00:57:30 +0000 Subject: Re: [v3,11/41] mips: reuse asm-generic/barrier.h Message-Id: <20160127005730.GE4503@linux.vnet.ibm.com> List-Id: References: <20160118081929.GA30420@gondor.apana.org.au> <20160118154629.GB3818@linux.vnet.ibm.com> <20160126165207.GB6029@fixme-laptop.cn.ibm.com> <20160126172227.GG6357@twins.programming.kicks-ass.net> <20160126201037.GU4503@linux.vnet.ibm.com> <20160126232921.GY4503@linux.vnet.ibm.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Linus Torvalds Cc: linux-mips , "linux-ia64@vger.kernel.org" , "Michael S. Tsirkin" , Peter Zijlstra , Will Deacon , virtualization , Peter Anvin , sparclinux@vger.kernel.org, Ingo Molnar , "linux-arch@vger.kernel.org" , linux-s390 , Russell King - ARM Linux , Herbert Xu , linux-sh@vger.kernel.org, Michael Ellerman , the arch/x86 maintainers , xen-devel@lists.xenproject.org, Ingo Molnar , linux-xtensa@linux-xtensa.org, James Hogan , uml-devel , Stefano Stabellini On Tue, Jan 26, 2016 at 03:45:23PM -0800, Linus Torvalds wrote: > On Tue, Jan 26, 2016 at 3:29 PM, Paul E. McKenney > wrote: > > > > No trailing data-dependent read, so agreed, no smp_read_barrier_depends() > > needed. That said, I believe that we should encourage rcu_dereference*() > > or lockless_dereference() instead of READ_ONCE() for documentation > > reasons, though. > > I agree that that is likely the right thing to do in pretty much all situations. > > In theory, there might be performance situations where we'd want to > actively avoid the smp_read_barrier_depends() inherent in those, but > considering that it's only a performance issue on alpha, and we > probably have all of two or three people using Linux on alpha, it's a > pretty theoretical performance worry. Agreed! Thanx, Paul