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 8AADFC1B0F2 for ; Wed, 20 Jun 2018 10:16:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4CFC3208B0 for ; Wed, 20 Jun 2018 10:16:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4CFC3208B0 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 S1754061AbeFTKQx (ORCPT ); Wed, 20 Jun 2018 06:16:53 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:59753 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753930AbeFTKQw (ORCPT ); Wed, 20 Jun 2018 06:16:52 -0400 Received: from p4fea482e.dip0.t-ipconnect.de ([79.234.72.46] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1fVaAG-0003AF-Rb; Wed, 20 Jun 2018 12:16:37 +0200 Date: Wed, 20 Jun 2018 12:16:36 +0200 (CEST) From: Thomas Gleixner To: Feng Tang cc: Pavel Tatashin , steven.sistare@oracle.com, daniel.m.jordan@oracle.com, linux@armlinux.org.uk, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, john.stultz@linaro.org, sboyd@codeaurora.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com, douly.fnst@cn.fujitsu.com, peterz@infradead.org, prarit@redhat.com, pmladek@suse.com, gnomes@lxorguk.ukuu.org.uk Subject: Re: [PATCH v10 7/7] x86/tsc: use tsc early In-Reply-To: <20180620101241.5vhmyvdjbenldp4r@shbuild888> Message-ID: References: <20180615174204.30581-1-pasha.tatashin@oracle.com> <20180615174204.30581-8-pasha.tatashin@oracle.com> <20180620101241.5vhmyvdjbenldp4r@shbuild888> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 20 Jun 2018, Feng Tang wrote: > On Wed, Jun 20, 2018 at 01:52:10AM +0200, Thomas Gleixner wrote: > > > > static DEFINE_STATIC_KEY_FALSE(__use_tsc); > > +static DEFINE_STATIC_KEY_TRUE(tsc_early_enabled); > > One potential problem may be the several static_keys used here, > the "__use_tsc", the "__sched_clock_stable", it may not be used > very early in boot phase. As the the static_branch_enable() will > use pageing related code while the paging is not setup ready yet. I know how static keys work and thats the reason for having the extra conditional. The key is disabled at a point where paging is available. > > /* > > * Scheduler clock - returns current time in nanosec units. > > */ > > u64 native_sched_clock(void) > > { > > - if (static_branch_likely(&__use_tsc)) { > > - u64 tsc_now = rdtsc(); > > + if (static_branch_likely(&__use_tsc)) > > + return cycles_2_ns(rdtsc()); > > > > - /* return the value in ns */ > > - return cycles_2_ns(tsc_now); > > + if (static_branch_unlikely(&tsc_early_enabled)) { > > + if (tsc_early_sched_clock) > > + return cycles_2_ns(rdtsc()); > > } Thanks, tglx