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=-0.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,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 3B67CC31E4D for ; Fri, 14 Jun 2019 15:59:47 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1EB1F2168B for ; Fri, 14 Jun 2019 15:59:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1EB1F2168B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id E85DE1540; Fri, 14 Jun 2019 15:59:46 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 4FCA91531 for ; Fri, 14 Jun 2019 15:59:46 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from Galois.linutronix.de (Galois.linutronix.de [146.0.238.70]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 2BFCAE5 for ; Fri, 14 Jun 2019 15:59:45 +0000 (UTC) Received: from [5.158.153.52] (helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hboc2-0002RQ-MH; Fri, 14 Jun 2019 17:59:34 +0200 Date: Fri, 14 Jun 2019 17:59:34 +0200 (CEST) From: Thomas Gleixner To: Ricardo Neri Subject: Re: [RFC PATCH v4 03/21] x86/hpet: Calculate ticks-per-second in a separate function In-Reply-To: Message-ID: References: <1558660583-28561-1-git-send-email-ricardo.neri-calderon@linux.intel.com> <1558660583-28561-4-git-send-email-ricardo.neri-calderon@linux.intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Cc: Kate Stewart , "Ravi V. Shankar" , x86@kernel.org, Ashok Raj , Arnd Bergmann , Peter Zijlstra , Philippe Ombredanne , Randy Dunlap , Clemens Ladisch , linux-kernel@vger.kernel.org, Stephane Eranian , Ricardo Neri , "Rafael J. Wysocki" , iommu@lists.linux-foundation.org, Tony Luck , "H. Peter Anvin" , Andi Kleen , Borislav Petkov , Ingo Molnar X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On Fri, 14 Jun 2019, Thomas Gleixner wrote: > On Thu, 23 May 2019, Ricardo Neri wrote: > > int hpet_alloc(struct hpet_data *hdp) > > { > > u64 cap, mcfg; > > @@ -844,7 +867,6 @@ int hpet_alloc(struct hpet_data *hdp) > > struct hpets *hpetp; > > struct hpet __iomem *hpet; > > static struct hpets *last; > > - unsigned long period; > > unsigned long long temp; > > u32 remainder; > > > > @@ -894,12 +916,7 @@ int hpet_alloc(struct hpet_data *hdp) > > > > last = hpetp; > > > > - period = (cap & HPET_COUNTER_CLK_PERIOD_MASK) >> > > - HPET_COUNTER_CLK_PERIOD_SHIFT; /* fs, 10^-15 */ > > - temp = 1000000000000000uLL; /* 10^15 femtoseconds per second */ > > - temp += period >> 1; /* round */ > > - do_div(temp, period); > > - hpetp->hp_tick_freq = temp; /* ticks per second */ > > + hpetp->hp_tick_freq = hpet_get_ticks_per_sec(cap); > > Why are we actually computing this over and over? > > In hpet_enable() which is the first function invoked we have: > > /* > * The period is a femto seconds value. Convert it to a > * frequency. > */ > freq = FSEC_PER_SEC; > do_div(freq, hpet_period); > hpet_freq = freq; > > So we already have ticks per second, aka frequency, right? So why do we > need yet another function instead of using the value which is computed > once? The frequency of the HPET channels has to be identical no matter > what. If it's not HPET is broken beyond repair. Aside of that this change breaks the IA64 support for /dev/hpet. Thanks, tglx _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu