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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 EB6D3C00A89 for ; Fri, 30 Oct 2020 22:16:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8DD4222228 for ; Fri, 30 Oct 2020 22:16:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725832AbgJ3WQe convert rfc822-to-8bit (ORCPT ); Fri, 30 Oct 2020 18:16:34 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:48661 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725774AbgJ3WQe (ORCPT ); Fri, 30 Oct 2020 18:16:34 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-61-f8gWZUeEPIy3ZCB6ot-DsQ-1; Fri, 30 Oct 2020 22:16:29 +0000 X-MC-Unique: f8gWZUeEPIy3ZCB6ot-DsQ-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, 30 Oct 2020 22:16:29 +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, 30 Oct 2020 22:16:29 +0000 From: David Laight To: 'Benjamin Segall' , Hui Su CC: "mingo@redhat.com" , "peterz@infradead.org" , "juri.lelli@redhat.com" , "vincent.guittot@linaro.org" , "dietmar.eggemann@arm.com" , "rostedt@goodmis.org" , "mgorman@suse.de" , "bristot@redhat.com" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] sched/fair: remove the spin_lock operations Thread-Topic: [PATCH] sched/fair: remove the spin_lock operations Thread-Index: AQHWru02j9v+7b8fw0CwtF3P4oRlh6mwtROg Date: Fri, 30 Oct 2020 22:16:29 +0000 Message-ID: <22f99ee1d9b245c2a356d4d555b54e6a@AcuMS.aculab.com> References: <20201030144621.GA96974@rlk> In-Reply-To: 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: linux-kernel@vger.kernel.org From: Benjamin Segall > Sent: 30 October 2020 18:48 > > Hui Su writes: > > > Since 'ab93a4bc955b ("sched/fair: Remove > > distribute_running fromCFS bandwidth")',there is > > nothing to protect between raw_spin_lock_irqsave/store() > > in do_sched_cfs_slack_timer(). > > > > So remove it. > > Reviewed-by: Ben Segall > > (I might nitpick the subject to be clear that it should be trivial > because the lock area is empty, or call them dead or something, but it's > not all that important) I don't know about this case, but a lock+unlock can be used to ensure that nothing else holds the lock when acquiring the lock requires another lock be held. So if the normal sequence is: lock(table) # lookup item lock(item) unlock(table) .... unlock(item) Then it can make sense to do: lock(table) lock(item) unlock(item) .... unlock(table) although that ought to deserve a comment. avid - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)