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 83940C4646A for ; Wed, 12 Sep 2018 14:20:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3831820882 for ; Wed, 12 Sep 2018 14:20:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3831820882 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1727676AbeILTZE (ORCPT ); Wed, 12 Sep 2018 15:25:04 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:48754 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726677AbeILTZD (ORCPT ); Wed, 12 Sep 2018 15:25:03 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5498287AA9; Wed, 12 Sep 2018 14:20:20 +0000 (UTC) Received: from oldenburg.str.redhat.com (dhcp-192-212.str.redhat.com [10.33.192.212]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 81E99FA981; Wed, 12 Sep 2018 14:20:16 +0000 (UTC) Subject: Re: [PATCH v3] x86/vdso: Handle clock_gettime(CLOCK_TAI) in vDSO To: Thomas Gleixner Cc: Andy Lutomirski , Matt Rickard , Stephen Boyd , John Stultz , X86 ML , LKML References: <20180901015935.CCF0B18E20A9@virtux64.softrans.com.au> From: Florian Weimer Message-ID: <59403142-1073-3926-65dd-ac55ead357b9@redhat.com> Date: Wed, 12 Sep 2018 16:20:15 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Wed, 12 Sep 2018 14:20:20 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Wed, 12 Sep 2018 14:20:20 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'fweimer@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/12/2018 04:17 PM, Thomas Gleixner wrote: > On Wed, 12 Sep 2018, Florian Weimer wrote: >> On 09/09/2018 10:05 PM, Thomas Gleixner wrote: >>> See the patch below. It's integrating TAI without slowing down everything >>> and it definitely does not result in indirect calls. >>> >>> On a HSW it slows down clock_gettime() by ~0.5ns. On a SKL I get a speedup >>> by ~0.5ns. On a AMD Epyc server it's 1.2ns speedup. So it somehow depends >>> on the uarch and I also observed compiler version dependend variations. >> >> Does this mean glibc can keep using a single vDSO entrypoint, the one we >> have today? > > We have no intention to change that. Okay, I was wondering because Andy seemed to have proposed just that. > But we surely could provide separate entry points as an extra to avoid a > bunch of conditionals. We could adjust to that, but the benefit would be long-term because it's an ABI change for glibc, and they tend to take a long time to propagate. But I must say that clock_gettime is an odd place to start. I would have expected any of the type-polymorphic multiplexer interfaces (fcntl, ioctl, ptrace, futex) to be a more natural starting point. 8-) Thanks, Florian