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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 F31C7C64EB8 for ; Thu, 4 Oct 2018 21:09:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ACC292087D for ; Thu, 4 Oct 2018 21:09:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org ACC292087D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.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 S1727185AbeJEEE4 (ORCPT ); Fri, 5 Oct 2018 00:04:56 -0400 Received: from terminus.zytor.com ([198.137.202.136]:50709 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725758AbeJEEEz (ORCPT ); Fri, 5 Oct 2018 00:04:55 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id w94L94RE2885324 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Thu, 4 Oct 2018 14:09:04 -0700 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id w94L94qt2885321; Thu, 4 Oct 2018 14:09:04 -0700 Date: Thu, 4 Oct 2018 14:09:04 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Thomas Gleixner Message-ID: Cc: pbonzini@redhat.com, vkuznets@redhat.com, linux-kernel@vger.kernel.org, jgross@suse.com, matt@softrans.com.au, mingo@kernel.org, fweimer@redhat.com, arnd@arndb.de, hpa@zytor.com, sboyd@kernel.org, kys@microsoft.com, tglx@linutronix.de, john.stultz@linaro.org, peterz@infradead.org, luto@kernel.org Reply-To: arnd@arndb.de, fweimer@redhat.com, mingo@kernel.org, matt@softrans.com.au, vkuznets@redhat.com, linux-kernel@vger.kernel.org, jgross@suse.com, pbonzini@redhat.com, tglx@linutronix.de, kys@microsoft.com, sboyd@kernel.org, hpa@zytor.com, peterz@infradead.org, john.stultz@linaro.org, luto@kernel.org In-Reply-To: <20180917130707.741440803@linutronix.de> References: <20180917130707.741440803@linutronix.de> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/vdso] x86/vdso: Move cycle_last handling into the caller Git-Commit-ID: 3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7 Gitweb: https://git.kernel.org/tip/3e89bf35ebf59c12e8c1476f6681fae0ebdcb2a7 Author: Thomas Gleixner AuthorDate: Mon, 17 Sep 2018 14:45:43 +0200 Committer: Thomas Gleixner CommitDate: Thu, 4 Oct 2018 23:00:27 +0200 x86/vdso: Move cycle_last handling into the caller Dereferencing gtod->cycle_last all over the place and foing the cycles < last comparison in the vclock read functions generates horrible code. Doing it at the call site is much better and gains a few cycles both for TSC and pvclock. Caveat: This adds the comparison to the hyperv vclock as well, but I have no way to test that. Signed-off-by: Thomas Gleixner Acked-by: Andy Lutomirski Cc: Peter Zijlstra Cc: Matt Rickard Cc: Stephen Boyd Cc: John Stultz Cc: Florian Weimer Cc: "K. Y. Srinivasan" Cc: Vitaly Kuznetsov Cc: devel@linuxdriverproject.org Cc: virtualization@lists.linux-foundation.org Cc: Paolo Bonzini Cc: Arnd Bergmann Cc: Juergen Gross Link: https://lkml.kernel.org/r/20180917130707.741440803@linutronix.de --- arch/x86/entry/vdso/vclock_gettime.c | 39 +++++++----------------------------- 1 file changed, 7 insertions(+), 32 deletions(-) diff --git a/arch/x86/entry/vdso/vclock_gettime.c b/arch/x86/entry/vdso/vclock_gettime.c index 40105024a210..b7ccbff26a3f 100644 --- a/arch/x86/entry/vdso/vclock_gettime.c +++ b/arch/x86/entry/vdso/vclock_gettime.c @@ -77,9 +77,8 @@ static notrace const struct pvclock_vsyscall_time_info *get_pvti0(void) static notrace u64 vread_pvclock(void) { const struct pvclock_vcpu_time_info *pvti = &get_pvti0()->pvti; - u64 ret; - u64 last; u32 version; + u64 ret; /* * Note: The kernel and hypervisor must guarantee that cpu ID @@ -112,13 +111,7 @@ static notrace u64 vread_pvclock(void) ret = __pvclock_read_cycles(pvti, rdtsc_ordered()); } while (pvclock_read_retry(pvti, version)); - /* refer to vread_tsc() comment for rationale */ - last = gtod->cycle_last; - - if (likely(ret >= last)) - return ret; - - return last; + return ret; } #endif #ifdef CONFIG_HYPERV_TSCPAGE @@ -131,30 +124,10 @@ static notrace u64 vread_hvclock(void) } #endif -notrace static u64 vread_tsc(void) -{ - u64 ret = (u64)rdtsc_ordered(); - u64 last = gtod->cycle_last; - - if (likely(ret >= last)) - return ret; - - /* - * GCC likes to generate cmov here, but this branch is extremely - * predictable (it's just a function of time and the likely is - * very likely) and there's a data dependence, so force GCC - * to generate a branch instead. I don't barrier() because - * we don't actually need a barrier, and if this function - * ever gets inlined it will generate worse code. - */ - asm volatile (""); - return last; -} - notrace static inline u64 vgetcyc(int mode) { if (mode == VCLOCK_TSC) - return vread_tsc(); + return (u64)rdtsc_ordered(); #ifdef CONFIG_PARAVIRT_CLOCK else if (mode == VCLOCK_PVCLOCK) return vread_pvclock(); @@ -169,17 +142,19 @@ notrace static inline u64 vgetcyc(int mode) notrace static int do_hres(clockid_t clk, struct timespec *ts) { struct vgtod_ts *base = >od->basetime[clk]; + u64 cycles, last, ns; unsigned int seq; - u64 cycles, ns; do { seq = gtod_read_begin(gtod); ts->tv_sec = base->sec; ns = base->nsec; + last = gtod->cycle_last; cycles = vgetcyc(gtod->vclock_mode); if (unlikely((s64)cycles < 0)) return vdso_fallback_gettime(clk, ts); - ns += (cycles - gtod->cycle_last) * gtod->mult; + if (cycles > last) + ns += (cycles - last) * gtod->mult; ns >>= gtod->shift; } while (unlikely(gtod_read_retry(gtod, seq)));