From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941236AbcIZN2u (ORCPT ); Mon, 26 Sep 2016 09:28:50 -0400 Received: from mail-dm3nam03on0078.outbound.protection.outlook.com ([104.47.41.78]:22496 "EHLO NAM03-DM3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S935875AbcIZN2s (ORCPT ); Mon, 26 Sep 2016 09:28:48 -0400 Authentication-Results: spf=pass (sender IP is 63.163.107.225) smtp.mailfrom=sandisk.com; vger.kernel.org; dkim=none (message not signed) header.d=none;vger.kernel.org; dmarc=bestguesspass action=none header.from=sandisk.com; X-AuditID: 0ac94371-5f3ff7000000f08d-15-57e920832309 Subject: Re: [PATCH] sched: Change READ_ONCE(jiffies) into jiffies To: Peter Zijlstra References: <20160926085547.GJ5012@twins.programming.kicks-ass.net> CC: Ingo Molnar , Oleg Nesterov , linux-kernel From: Bart Van Assche Message-ID: 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SpamDiagnosticMetadata: NSPM X-Microsoft-Exchange-Diagnostics: 1;CY1PR0201MB1516;20:UbBZsGtgNSyOljI0ed10KwFWJGKu9oPp8Agn04QuOOfisUfcJtZvwSQOYW8tmMYWXMoBVyjzVzt8p+arNSbwrfG1SRp+7sq9wHeIjTEjyMaVIt4+2JN5XU4uf7Miet7SSt86FaRvmhQtYa+K1T5VIP9b1Lz4PLGzPS10cS+6Swu+lZOIAvU73Ir8YH3UxyfoNvgsUnrColUilmABJ5omn3T6YhgIvF9V1phdVGaKXg529mmJcVp3agjGsithB/9B X-OriginatorOrg: sandisk.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Sep 2016 13:28:45.5959 (UTC) X-MS-Exchange-CrossTenant-Id: fcd9ea9c-ae8c-460c-ab3c-3db42d7ac64d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=fcd9ea9c-ae8c-460c-ab3c-3db42d7ac64d;Ip=[63.163.107.225];Helo=[milsmgep14.sandisk.com] X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY1PR0201MB1516 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/26/16 01:55, Peter Zijlstra wrote: > On Sun, Sep 25, 2016 at 07:08:45PM -0700, Bart Van Assche wrote: >> A quote from Documentation/memory_barriers.txt: >> >> For example, because 'jiffies' is marked volatile, it is never >> necessary to say READ_ONCE(jiffies). The reason for this is >> that READ_ONCE() and WRITE_ONCE() are implemented as volatile >> casts, which has no effect when its argument is already marked >> volatile. >> >> Hence change all 'READ_ONCE(jiffies)' occurrences into 'jiffies'. > > So I'm not a huge fan of this patch. Yes its technically pointless, but > it does convey intent. See the READ_ONCE() as a comment if you will. Hello Peter, Are you aware that the scheduler code is the only code that uses READ_ONCE() to read 'jiffies', and that even in the scheduler not all 'jiffies' reads use READ_ONCE()? This patch makes the scheduler code more consistent and easier to read without affecting the generated code. Bart.