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 Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CDB07C5475B for ; Fri, 8 Mar 2024 13:29:25 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.a=rsa-sha256 header.s=Intel header.b=bTRLqaaL; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Trn843YFgz3w58 for ; Sat, 9 Mar 2024 00:29:24 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.a=rsa-sha256 header.s=Intel header.b=bTRLqaaL; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=intel.com (client-ip=192.198.163.9; helo=mgamail.intel.com; envelope-from=adrian.hunter@intel.com; receiver=lists.ozlabs.org) Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.9]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4TrmtQ4pJyz3vZj for ; Sat, 9 Mar 2024 00:17:34 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1709903855; x=1741439855; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=qOOcsyBxpUsFxkAH1hi2UNpYCz2148dQEbBRMVKVw/4=; b=bTRLqaaLjH5nyzuzj+aiF7S3sBzufTyts+Lq9r9Swr7TQ19nXAlql7qO micXf7dOSt6px58/igy3CaMmWjZFxSW49YvxixD2TE5p6Zj+WwohWF08T G0Rn6Gw14Cg0R+ctC3xXA8L5BBA/i6f/Zdzy2nFhGgEooEVdqoWQI0xk2 nL/xmyhHoM2ACcLHkRf8St2AvObaMOf1qOSY2zSoOwWGBrhictWHW4TPl 1k8zLnNuG8ZOUsLEoPZ+LMEl6bzooTNrJSAFUjtW/H0cU7khtUlNjBdA4 Bp4oR8O8/MNgiLJCKNzigJF6XoBJwr9JtiwjO+acUT8CHmSin+BEXQ63w Q==; X-IronPort-AV: E=McAfee;i="6600,9927,11006"; a="15342933" X-IronPort-AV: E=Sophos;i="6.07,109,1708416000"; d="scan'208";a="15342933" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Mar 2024 05:17:32 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,109,1708416000"; d="scan'208";a="15161611" Received: from ahunter6-mobl1.ger.corp.intel.com (HELO ahunter-VirtualBox.home\044ger.corp.intel.com) ([10.249.46.63]) by orviesa005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Mar 2024 05:17:25 -0800 From: Adrian Hunter To: Thomas Gleixner Subject: [PATCH 18/19] timekeeping: Let timekeeping_cycles_to_ns() handle both under and overflow Date: Fri, 8 Mar 2024 15:15:11 +0200 Message-Id: <20240308131512.44324-19-adrian.hunter@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240308131512.44324-1-adrian.hunter@intel.com> References: <20240308131512.44324-1-adrian.hunter@intel.com> MIME-Version: 1.0 Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Zijlstra , Dave Hansen , John Stultz , "H. Peter Anvin" , Alexander Gordeev , Vincenzo Frascino , linux-s390@vger.kernel.org, Arnd Bergmann , x86@kernel.org, "Aneesh Kumar K.V" , Ingo Molnar , "Naveen N. Rao" , Christian Borntraeger , Vasily Gorbik , Heiko Carstens , Nicholas Piggin , Borislav Petkov , Andy Lutomirski , Bjorn Helgaas , Anna-Maria Behnsen , Stephen Boyd , Randy Dunlap , linux-kernel@vger.kernel.org, Sven Schnelle , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" For the case !CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE, forego overflow protection in the range (mask << 1) < delta <= mask, and interpret it always as an inconsistency between CPU clock values. That allows slightly neater code, and it is on a slow path so has no effect on performance. Suggested-by: Thomas Gleixner Signed-off-by: Adrian Hunter --- kernel/time/timekeeping.c | 31 +++++++++++++------------------ 1 file changed, 13 insertions(+), 18 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 111dfdbd488f..4e18db1819f8 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -266,17 +266,14 @@ static inline u64 timekeeping_debug_get_ns(const struct tk_read_base *tkr) * Try to catch underflows by checking if we are seeing small * mask-relative negative values. */ - if (unlikely((~delta & mask) < (mask >> 3))) { + if (unlikely((~delta & mask) < (mask >> 3))) tk->underflow_seen = 1; - now = last; - } - /* Cap delta value to the max_cycles values to avoid mult overflows */ - if (unlikely(delta > max)) { + /* Check for multiplication overflows */ + if (unlikely(delta > max)) tk->overflow_seen = 1; - now = last + max; - } + /* timekeeping_cycles_to_ns() handles both under and overflow */ return timekeeping_cycles_to_ns(tkr, now); } #else @@ -375,19 +372,17 @@ static inline u64 timekeeping_cycles_to_ns(const struct tk_read_base *tkr, u64 c u64 mask = tkr->mask, delta = (cycles - tkr->cycle_last) & mask; /* - * This detects the case where the delta overflows the multiplication - * with tkr->mult. + * This detects both negative motion and the case where the delta + * overflows the multiplication with tkr->mult. */ if (unlikely(delta > tkr->clock->max_cycles)) { - if (IS_ENABLED(CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE)) { - /* - * Handle clocksource inconsistency between CPUs to prevent - * time from going backwards by checking for the MSB of the - * mask being set in the delta. - */ - if (unlikely(delta & ~(mask >> 1))) - return tkr->xtime_nsec >> tkr->shift; - } + /* + * Handle clocksource inconsistency between CPUs to prevent + * time from going backwards by checking for the MSB of the + * mask being set in the delta. + */ + if (delta & ~(mask >> 1)) + return tkr->xtime_nsec >> tkr->shift; return delta_to_ns_safe(tkr, delta); } -- 2.34.1