From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Date: Fri, 03 Jun 2016 22:34:17 +0000 Subject: Re: [RFC 10/12] x86, rwsem: simplify __down_write Message-Id: <20160603223417.GB3892@twins.programming.kicks-ass.net> List-Id: References: <1454444369-2146-1-git-send-email-mhocko@kernel.org> <1454444369-2146-11-git-send-email-mhocko@kernel.org> <20160203081016.GD32652@gmail.com> <20160603161339.GC3693@twins.programming.kicks-ass.net> In-Reply-To: <20160603161339.GC3693@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Ingo Molnar Cc: Michal Hocko , LKML , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , "David S. Miller" , Tony Luck , Andrew Morton , Chris Zankel , Max Filippov , x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Michal Hocko , Linus Torvalds , "Paul E. McKenney" , Jason Low On Fri, Jun 03, 2016 at 06:13:39PM +0200, Peter Zijlstra wrote: > So I've been playing with this again because Jason's atomic_long_t > patches made a mess of things. > > (similar findings for both ia64 and s390, suggesting killing all > arch/*/include/asm/rwsem.h might actuyally be an option). > Blergh; so looking at more asm there's still a few tricks we cannot do. So while overall size is down, some paths do end up more expensive. (It typically boils down to creative use of condition flags, which is very hard in C) From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752694AbcFCWej (ORCPT ); Fri, 3 Jun 2016 18:34:39 -0400 Received: from merlin.infradead.org ([205.233.59.134]:52454 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751727AbcFCWeg (ORCPT ); Fri, 3 Jun 2016 18:34:36 -0400 Date: Sat, 4 Jun 2016 00:34:17 +0200 From: Peter Zijlstra To: Ingo Molnar Cc: Michal Hocko , LKML , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , "David S. Miller" , Tony Luck , Andrew Morton , Chris Zankel , Max Filippov , x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Michal Hocko , Linus Torvalds , "Paul E. McKenney" , Jason Low Subject: Re: [RFC 10/12] x86, rwsem: simplify __down_write Message-ID: <20160603223417.GB3892@twins.programming.kicks-ass.net> References: <1454444369-2146-1-git-send-email-mhocko@kernel.org> <1454444369-2146-11-git-send-email-mhocko@kernel.org> <20160203081016.GD32652@gmail.com> <20160603161339.GC3693@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160603161339.GC3693@twins.programming.kicks-ass.net> 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 On Fri, Jun 03, 2016 at 06:13:39PM +0200, Peter Zijlstra wrote: > So I've been playing with this again because Jason's atomic_long_t > patches made a mess of things. > > (similar findings for both ia64 and s390, suggesting killing all > arch/*/include/asm/rwsem.h might actuyally be an option). > Blergh; so looking at more asm there's still a few tricks we cannot do. So while overall size is down, some paths do end up more expensive. (It typically boils down to creative use of condition flags, which is very hard in C)