Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753457AbdIDKcF convert rfc822-to-8bit (ORCPT ); Mon, 4 Sep 2017 06:32:05 -0400 Received: from mga01.intel.com ([192.55.52.88]:48455 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751321AbdIDKcD (ORCPT ); Mon, 4 Sep 2017 06:32:03 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.41,474,1498546800"; d="scan'208";a="1168929505" From: "Reshetova, Elena" To: Peter Zijlstra CC: Thomas Gleixner , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "gregkh@linuxfoundation.org" , "viro@zeniv.linux.org.uk" , "tj@kernel.org" , "mingo@redhat.com" , "hannes@cmpxchg.org" , "lizefan@huawei.com" , "acme@kernel.org" , "alexander.shishkin@linux.intel.com" , "eparis@redhat.com" , "akpm@linux-foundation.org" , "arnd@arndb.de" , "luto@kernel.org" , "keescook@chromium.org" , "dvhart@infradead.org" , "ebiederm@xmission.com" Subject: RE: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t Thread-Topic: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t Thread-Index: AQHTIYrzZIHADGwHSEu0EVkr0E9TAqKflyIAgAAhQgCAAAFJAIAAI4yQgAADB+CAAAkkgIAAGdsA///3mwCAABRlgIAASW8AgAQ1RNA= Date: Mon, 4 Sep 2017 10:31:54 +0000 Message-ID: <2236FBA76BA1254E88B949DDB74E612B6FF63ED7@IRSMSX102.ger.corp.intel.com> References: <1504095773-22895-1-git-send-email-elena.reshetova@intel.com> <1504095773-22895-15-git-send-email-elena.reshetova@intel.com> <20170901093852.it4d4bxoy2lmojrk@hirez.programming.kicks-ass.net> <2236FBA76BA1254E88B949DDB74E612B6FF6347F@IRSMSX102.ger.corp.intel.com> <20170901123415.s3fxlyeyourz47av@hirez.programming.kicks-ass.net> <2236FBA76BA1254E88B949DDB74E612B6FF63506@IRSMSX102.ger.corp.intel.com> <20170901133644.jf57pwuaep6zirxz@hirez.programming.kicks-ass.net> <2236FBA76BA1254E88B949DDB74E612B6FF6369D@IRSMSX102.ger.corp.intel.com> <20170901191234.ghybbmpm73miwmkp@hirez.programming.kicks-ass.net> In-Reply-To: <20170901191234.ghybbmpm73miwmkp@hirez.programming.kicks-ass.net> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-product: dlpe-windows dlp-version: 11.0.0.116 dlp-reaction: no-action x-originating-ip: [163.33.239.180] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2298 Lines: 50 > -----Original Message----- > From: Peter Zijlstra [mailto:peterz@infradead.org] > Sent: Friday, September 1, 2017 10:13 PM > To: Reshetova, Elena > Cc: Thomas Gleixner ; linux-kernel@vger.kernel.org; linux- > fsdevel@vger.kernel.org; gregkh@linuxfoundation.org; viro@zeniv.linux.org.uk; > tj@kernel.org; mingo@redhat.com; hannes@cmpxchg.org; lizefan@huawei.com; > acme@kernel.org; alexander.shishkin@linux.intel.com; eparis@redhat.com; > akpm@linux-foundation.org; arnd@arndb.de; luto@kernel.org; > keescook@chromium.org; dvhart@infradead.org; ebiederm@xmission.com > Subject: Re: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount_t > > On Fri, Sep 01, 2017 at 05:03:55PM +0000, Reshetova, Elena wrote: > > > On Fri, Sep 01, 2017 at 01:24:16PM +0000, Reshetova, Elena wrote: > > > > > > > > > On Fri, Sep 01, 2017 at 11:05:33AM +0000, Reshetova, Elena wrote: > > > > > > Actually on the second thought: does the above memory ordering > differences > > > > > > really apply when we have ARCH_HAS_REFCOUNT? To me it looks like the > way > > > > > > how it is currently implemented for x86 is the same way as it is for atomic > > > cases. > > > > > > > > > > Never look to x86 for memory ordering, its boring. > > > > > > > > > > And yes, for the ARM implementation it can certainly make a difference. > > > > > > > > So, yes, what I am trying to say is that it can really depend if you have > > > ARCH_HAS_REFCOUNT > > > > enabled or not and then also based on architecture. Thus I believe is also true > for > > > atomic: there > > > > might be differences when you use arch. dependent version of function or not. > > > > > > So the generic one in lib/refcount.c is already weaker on ARM, they > > > don't need to do a ARCH specific 'fast' implementation for the > > > difference to show up. > > > > But can they make "fast" implementation on ARM that would give stronger > memory guarantees? > > Whatever for? Well, maybe just by default when arch.-specific implementation is done. But I was just trying to speculate to understand. I will resend this one with new comment added. Still not sure if I need to resend the whole series with updated commits or break this up by individual patches further for the separate merges.