From patchwork Thu Jan 16 17:58:34 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Christophe Leroy X-Patchwork-Id: 11337505 X-Patchwork-Delegate: paulburton@kernel.org Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0A77D14B7 for ; Thu, 16 Jan 2020 17:58:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DC2CC24679 for ; Thu, 16 Jan 2020 17:58:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=c-s.fr header.i=@c-s.fr header.b="gxE//bpY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394634AbgAPR6v (ORCPT ); Thu, 16 Jan 2020 12:58:51 -0500 Received: from pegase1.c-s.fr ([93.17.236.30]:35922 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2394671AbgAPR6h (ORCPT ); Thu, 16 Jan 2020 12:58:37 -0500 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 47zBkx5Pynz9v4gt; Thu, 16 Jan 2020 18:58:33 +0100 (CET) Authentication-Results: localhost; dkim=pass reason="1024-bit key; insecure key" header.d=c-s.fr header.i=@c-s.fr header.b=gxE//bpY; dkim-adsp=pass; dkim-atps=neutral X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id jfl2bkZ8t9tf; Thu, 16 Jan 2020 18:58:33 +0100 (CET) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 47zBkx3Rwbz9v4gc; Thu, 16 Jan 2020 18:58:33 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=c-s.fr; s=mail; t=1579197513; bh=UFDJu66szbpL4Xw0xXz0xNV43kPco38dmpx+eBljPF4=; h=In-Reply-To:References:From:Subject:To:Cc:Date:From; b=gxE//bpYKFxAWuGDDXDIa3xdSWFzMMRq4FuxjO1eMSFN2a05pq5qLbwB0TN6BrWmJ ZnzwYy+g3jHvmO2BCygYehv9TiPmItAeN3sPUHsDnH/0B45RoA8w+Zipz7TfG4jVK+ 1LBc5voMUebWSGExFornSGTfsSHNAHbcf+37K/PM= Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 206E98B82A; Thu, 16 Jan 2020 18:58:35 +0100 (CET) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id X73jTLr1bjTq; Thu, 16 Jan 2020 18:58:35 +0100 (CET) Received: from po14934vm.idsi0.si.c-s.fr (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id C8E018B82D; Thu, 16 Jan 2020 18:58:34 +0100 (CET) Received: by po14934vm.idsi0.si.c-s.fr (Postfix, from userid 0) id 9F40364A33; Thu, 16 Jan 2020 17:58:34 +0000 (UTC) Message-Id: In-Reply-To: References: From: Christophe Leroy Subject: [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation To: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , nathanl@linux.ibm.com, arnd@arndb.de, tglx@linutronix.de, vincenzo.frascino@arm.com, luto@kernel.org Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, x86@kernel.org Date: Thu, 16 Jan 2020 17:58:34 +0000 (UTC) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On powerpc/32, GCC (8.1) generates pretty bad code for the ns >>= vd->shift operation taking into account that the shift is always < 32 and the upper part of the result is likely to be nul. GCC makes reversed assumptions considering the shift to be likely >= 32 and the upper part to be like not nul. unsigned long long shift(unsigned long long x, unsigned char s) { return x >> s; } results in: 00000018 : 18: 35 25 ff e0 addic. r9,r5,-32 1c: 41 80 00 10 blt 2c 20: 7c 64 4c 30 srw r4,r3,r9 24: 38 60 00 00 li r3,0 28: 4e 80 00 20 blr 2c: 54 69 08 3c rlwinm r9,r3,1,0,30 30: 21 45 00 1f subfic r10,r5,31 34: 7c 84 2c 30 srw r4,r4,r5 38: 7d 29 50 30 slw r9,r9,r10 3c: 7c 63 2c 30 srw r3,r3,r5 40: 7d 24 23 78 or r4,r9,r4 44: 4e 80 00 20 blr Even when forcing the shift with an &= 31, it still considers the shift as likely >= 32. Define a vdso_shift_ns() macro that can be overriden by arches. Signed-off-by: Christophe Leroy --- lib/vdso/gettimeofday.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 724b45c3e8ac..9ba92058cfd7 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -39,6 +39,13 @@ u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult) } #endif +#ifndef vdso_shift_ns +static __always_inline u64 vdso_shift_ns(u64 ns, unsigned long shift) +{ + return ns >> shift; +} +#endif + #ifndef __arch_vdso_hres_capable static inline bool __arch_vdso_hres_capable(void) { @@ -148,7 +155,7 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk, ns = vdso_ts->nsec; last = vd->cycle_last; ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult); - ns >>= vd->shift; + ns = vdso_shift_ns(ns, vd->shift); sec = vdso_ts->sec; } while (unlikely(vdso_read_retry(vd, seq)));