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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 2E57FC1B0D8 for ; Mon, 14 Dec 2020 08:18:29 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 C3FF7207A5 for ; Mon, 14 Dec 2020 08:18:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C3FF7207A5 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=ACULAB.COM Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 29EF66E0B8; Mon, 14 Dec 2020 08:17:42 +0000 (UTC) Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by gabe.freedesktop.org (Postfix) with ESMTPS id DE3616ECB9 for ; Fri, 11 Dec 2020 22:06:29 +0000 (UTC) Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-25-lRPy8p40M8CPiAlacIukIQ-1; Fri, 11 Dec 2020 22:06:25 +0000 X-MC-Unique: lRPy8p40M8CPiAlacIukIQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 11 Dec 2020 22:06:24 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Fri, 11 Dec 2020 22:06:24 +0000 From: David Laight To: 'Thomas Gleixner' , Tvrtko Ursulin , LKML Subject: RE: [patch 14/30] drm/i915/pmu: Replace open coded kstat_irqs() copy Thread-Topic: [patch 14/30] drm/i915/pmu: Replace open coded kstat_irqs() copy Thread-Index: AQHWz72qwjNpP0n0UkWT70W8RrLS8qnx7xrwgAB1jgCAAA6ksA== Date: Fri, 11 Dec 2020 22:06:24 +0000 Message-ID: <6dd2eb7de7ad4a5893f057b90662718f@AcuMS.aculab.com> References: <20201210192536.118432146@linutronix.de> <20201210194043.957046529@linutronix.de> <87y2i4h54i.fsf@nanos.tec.linutronix.de> <87eejwgib7.fsf@nanos.tec.linutronix.de> In-Reply-To: <87eejwgib7.fsf@nanos.tec.linutronix.de> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US X-Mailman-Approved-At: Mon, 14 Dec 2020 08:17:40 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Mark Rutland , Karthikeyan Mitran , Peter Zijlstra , Catalin Marinas , "dri-devel@lists.freedesktop.org" , Chris Wilson , "James E.J. Bottomley" , "netdev@vger.kernel.org" , Will Deacon , Michal Simek , "linux-s390@vger.kernel.org" , afzal mohammed , Lorenzo Pieralisi , Dave Jiang , "xen-devel@lists.xenproject.org" , Leon Romanovsky , "linux-rdma@vger.kernel.org" , Marc Zyngier , Helge Deller , Russell King , Christian Borntraeger , "linux-pci@vger.kernel.org" , Jakub Kicinski , Heiko Carstens , Wambui Karuga , Allen Hubbe , Juergen Gross , "intel-gfx@lists.freedesktop.org" , "linux-gpio@vger.kernel.org" , Stefano Stabellini , Rodrigo Vivi , Bjorn Helgaas , Lee Jones , "linux-arm-kernel@lists.infradead.org" , Boris Ostrovsky , David Airlie , "linux-parisc@vger.kernel.org" , Pankaj Bharadiya , Hou Zhiqiang , Tariq Toukan , Jon Mason , "linux-ntb@googlegroups.com" , Saeed Mahameed , "David S. Miller" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" From: Thomas Gleixner > Sent: 11 December 2020 21:11 > > On Fri, Dec 11 2020 at 14:19, David Laight wrote: > > From: Thomas Gleixner > >> You can't catch that. If this really becomes an issue you need a > >> sequence counter around it. > > > > Or just two copies of the high word. > > Provided the accesses are sequenced: > > writer: > > load high:low > > add small_value,high:low > > store high > > store low > > store high_copy > > reader: > > load high_copy > > load low > > load high > > if (high != high_copy) > > low = 0; > > And low = 0 is solving what? You need to loop back and retry until it's > consistent and then it's nothing else than an open coded sequence count. If it is a counter or timestamp then the high:0 value happened some time between when you started trying to read the value and when you finished trying to read it. As such it is a perfectly reasonable return value. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales) _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel