From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933011AbbJIHcM (ORCPT ); Fri, 9 Oct 2015 03:32:12 -0400 Received: from mail-wi0-f171.google.com ([209.85.212.171]:36296 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932927AbbJIHcK (ORCPT ); Fri, 9 Oct 2015 03:32:10 -0400 Date: Fri, 9 Oct 2015 09:32:06 +0200 From: Ingo Molnar To: Andy Lutomirski Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Brian Gerst , Denys Vlasenko , Linus Torvalds , Borislav Petkov Subject: Re: [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall arg fetch Message-ID: <20151009073206.GB31859@gmail.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Andy Lutomirski wrote: > we're following a 32-bit pointer, and the uaccess code isn't smart > enough to figure out that the access_ok check isn't needed. > > This saves about three cycles on a cache-hot fast syscall. Another request: could you please stick the benchmarking code of the various x86 system call variants into 'perf bench' - under tools/perf/bench/, so that measurements can be done on more hardware and can be reproduced easily? I'd suggest we dedicate an entirely new benchmark family to it: 'perf bench x86' and then have: perf bench x86 syscall vdso perf bench x86 syscall int80 perf bench x86 syscall vdso-compat or so? ( I have some perf bench cleanups in -tip, so if you do this please base it on top of that. ) Thanks, Ingo