From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753035AbbFDKHn (ORCPT ); Thu, 4 Jun 2015 06:07:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49968 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752905AbbFDKHf (ORCPT ); Thu, 4 Jun 2015 06:07:35 -0400 Message-ID: <55702363.7090108@redhat.com> Date: Thu, 04 Jun 2015 12:07:31 +0200 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Josh Triplett CC: Ingo Molnar , Linus Torvalds , Steven Rostedt , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski , Oleg Nesterov , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] x86/asm/entry/32: Remove unnecessary optimization in stub32_clone References: <1433339930-20880-1-git-send-email-dvlasenk@redhat.com> <1433339930-20880-2-git-send-email-dvlasenk@redhat.com> <20150603163856.GA1744@x> In-Reply-To: <20150603163856.GA1744@x> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/03/2015 06:38 PM, Josh Triplett wrote: > On Wed, Jun 03, 2015 at 03:58:50PM +0200, Denys Vlasenko wrote: >> Really swap arguments #4 and #5 in stub32_clone instead of "optimizing" >> it into a move. >> >> Yes, tls_val is currently unused. Yes, on some CPUs XCHG is a little bit >> more expensive than MOV. But a cycle or two on an expensive syscall like >> clone() is way below noise floor, and this optimization is simply not worth >> the obfuscation of logic. > [...] >> This is a resend. >> >> There was a patch by Josh Triplett >> "x86: Opt into HAVE_COPY_THREAD_TLS, for both 32-bit and 64-bit" >> sent on May 11, >> which does the same thing as part of a bigger cleanup. >> He was supportive of this patch because of comments. >> He will simply have to drop one hunk from his patch. > > Strictly speaking, nothing needs this until clone starts paying > attention to its tls argument, which only happens in my cleanup series > that includes this change. So what's the purpose of driving this patch > separately? You wanted my comments in this patch to go in: On 04/22/2015 07:10 PM, Josh Triplett wrote: > I do think my two-patch HAVE_COPY_THREAD_TLS series should go in fixing > this, but I'd like to see the final version of Denys' comment added on > top of it (with an update to the type and name of the tls argument to > match the changes to sys_clone). If your patch will go in first, I'll send a patch adding only the comment. Since for now your patch did not make it yet, I'm submitting a patch which adds both a comment and the insn change. -- vda