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,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 6E3E4FC6182 for ; Fri, 14 Sep 2018 12:52:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3280220881 for ; Fri, 14 Sep 2018 12:52:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3280220881 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 S1728352AbeINSG1 (ORCPT ); Fri, 14 Sep 2018 14:06:27 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:49613 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728314AbeINSG0 (ORCPT ); Fri, 14 Sep 2018 14:06:26 -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 1g0nZr-0005wk-L8; Fri, 14 Sep 2018 14:52:03 +0200 Message-Id: <20180914125118.998589817@linutronix.de> User-Agent: quilt/0.65 Date: Fri, 14 Sep 2018 14:50:16 +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 10/11] x86/vdso: Move cycle_last handling into the caller References: <20180914125006.349747096@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=x86-vdso--Move-cycle_last-handling-into-the-caller.patch Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- arch/x86/entry/vdso/vclock_gettime.c | 39 ++++++----------------------------- 1 file changed, 7 insertions(+), 32 deletions(-) --- a/arch/x86/entry/vdso/vclock_gettime.c +++ b/arch/x86/entry/vdso/vclock_gettime.c @@ -76,9 +76,8 @@ static notrace const struct pvclock_vsys 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 @@ -111,13 +110,7 @@ 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 @@ -130,30 +123,10 @@ 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(); @@ -168,17 +141,19 @@ notrace static inline u64 vgetcyc(int mo 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)));