Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754567AbbG3Qej (ORCPT ); Thu, 30 Jul 2015 12:34:39 -0400 Received: from casper.infradead.org ([85.118.1.10]:55965 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752337AbbG3Qei (ORCPT ); Thu, 30 Jul 2015 12:34:38 -0400 Date: Thu, 30 Jul 2015 18:34:27 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, dave@stgolabs.net, waiman.long@hp.com Subject: Re: [PATCH tip/core/rcu 19/19] rcu: Add fastpath bypassing funnel locking Message-ID: <20150730163427.GO25159@twins.programming.kicks-ass.net> References: <20150717232901.GA22511@linux.vnet.ibm.com> <1437175764-24096-1-git-send-email-paulmck@linux.vnet.ibm.com> <1437175764-24096-19-git-send-email-paulmck@linux.vnet.ibm.com> <20150730144455.GZ19282@twins.programming.kicks-ass.net> <20150730153452.GG27280@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150730153452.GG27280@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 818 Lines: 17 On Thu, Jul 30, 2015 at 08:34:52AM -0700, Paul E. McKenney wrote: > On Thu, Jul 30, 2015 at 04:44:55PM +0200, Peter Zijlstra wrote: > > If the extra read before the cmpxchg() does not hurt, we should do the > > same for mutex and make the above redundant. > > I am pretty sure that different hardware wants it done differently. :-/ I think that most archs won't notice since any RmW includes a load of that variable anyhow. The only case where it can matter is if the RmW is done outside of the normal cache hierarchy -- like on Power, where the ll/sc bypasses the L1. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/