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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4220CCA47E for ; Wed, 8 Jun 2022 10:30:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236664AbiFHKaV convert rfc822-to-8bit (ORCPT ); Wed, 8 Jun 2022 06:30:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40928 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237739AbiFHK3V (ORCPT ); Wed, 8 Jun 2022 06:29:21 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 43222290B36 for ; Wed, 8 Jun 2022 03:18:26 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-272-XX68EoR1PGKPNiM1bBGKiQ-1; Wed, 08 Jun 2022 11:18:23 +0100 X-MC-Unique: XX68EoR1PGKPNiM1bBGKiQ-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.36; Wed, 8 Jun 2022 11:18:22 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.036; Wed, 8 Jun 2022 11:18:22 +0100 From: David Laight To: 'Eric Dumazet' , "David S . Miller" , Jakub Kicinski , Paolo Abeni CC: netdev , "Jason A . Donenfeld" , Eric Dumazet Subject: RE: [PATCH net-next 1/9] vlan: adopt u64_stats_t Thread-Topic: [PATCH net-next 1/9] vlan: adopt u64_stats_t Thread-Index: AQHYes4gtiuM5BJQbEG+qrM/apt4lK1FSwAw Date: Wed, 8 Jun 2022 10:18:22 +0000 Message-ID: References: <20220607233614.1133902-1-eric.dumazet@gmail.com> <20220607233614.1133902-2-eric.dumazet@gmail.com> In-Reply-To: <20220607233614.1133902-2-eric.dumazet@gmail.com> 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 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Eric Dumazet > Sent: 08 June 2022 00:36 > > As explained in commit 316580b69d0a ("u64_stats: provide u64_stats_t type") > we should use u64_stats_t and related accessors to avoid load/store tearing. > > Add READ_ONCE() when reading rx_errors & tx_dropped. Isn't this all getting entirely stupid? AFAICT nearly every 'memory' access in the kernel is going to get wrapped in READ/WRITE_ONCE() to avoid something that really never actually happens? It might be better to just mark everything 'volatile'. Although perhaps that ought to be a compiler option. OTOH I've seen gcc generate extra instructions for 'volatile' accesses - to the point where I used 'barrier()' to optimise code. I think the volatile casts in READ_ONCE() can generate worse code than volatile variables. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)