From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7EDF7ECDFD0 for ; Fri, 14 Sep 2018 12:52:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4128220881 for ; Fri, 14 Sep 2018 12:52:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4128220881 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728200AbeINSGU (ORCPT ); Fri, 14 Sep 2018 14:06:20 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:49572 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728089AbeINSGU (ORCPT ); Fri, 14 Sep 2018 14:06:20 -0400 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1g0nZk-0005vn-BM; Fri, 14 Sep 2018 14:51:56 +0200 Message-Id: <20180914125006.349747096@linutronix.de> User-Agent: quilt/0.65 Date: Fri, 14 Sep 2018 14:50:06 +0200 From: Thomas Gleixner To: LKML Cc: Andy Lutomirski , x86@kernel.org, Peter Zijlstra , Matt Rickard , Stephen Boyd , John Stultz , Florian Weimer , "K. Y. Srinivasan" , Vitaly Kuznetsov , devel@linuxdriverproject.org, virtualization@lists.linux-foundation.org, Paolo Bonzini , Arnd Bergmann , Juergen Gross Subject: [patch 00/11] x86/vdso: Cleanups, simmplifications and CLOCK_TAI support Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Matt attempted to add CLOCK_TAI support to the VDSO clock_gettime() implementation, which extended the clockid switch case and added yet another slightly different copy of the same code. Especially the extended switch case is problematic as the compiler tends to generate a jump table which then requires to use retpolines. If jump tables are disabled it adds yet another conditional to the existing maze. This series takes a different approach by consolidating the almost identical functions into one implementation for high resolution clocks and one for the coarse grained clock ids by storing the base data for each clock id in an array which is indexed by the clock id. This completely eliminates the switch case and allows further simplifications of the code base, which at the end all together gain a few cycles performance or at least stay on par with todays code. The resulting performance depends heavily on the micro architecture and the compiler. Thanks, tglx 8<------------------- arch/x86/Kconfig | 1 arch/x86/entry/vdso/vclock_gettime.c | 199 ++++++++------------------------ arch/x86/entry/vsyscall/vsyscall_gtod.c | 55 ++++---- arch/x86/include/asm/vgtod.h | 46 ++++--- arch/x86/kernel/time.c | 22 +++ include/linux/clocksource.h | 5 kernel/time/Kconfig | 4 kernel/time/clocksource.c | 2 8 files changed, 144 insertions(+), 190 deletions(-)