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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 515EAC43219 for ; Fri, 3 May 2019 14:37:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 23E9C2087F for ; Fri, 3 May 2019 14:37:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727107AbfECOh2 convert rfc822-to-8bit (ORCPT ); Fri, 3 May 2019 10:37:28 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:40224 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725809AbfECOh1 (ORCPT ); Fri, 3 May 2019 10:37:27 -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-111-sL2PkElbOGaMQnzoKPsUGw-1; Fri, 03 May 2019 15:37:22 +0100 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b::d117) by AcuMS.aculab.com (fd9f:af1c:a25b::d117) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Fri, 3 May 2019 15:37:21 +0100 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, 3 May 2019 15:37:21 +0100 From: David Laight To: 'Peter Zijlstra' , Waiman Long CC: Ingo Molnar , Will Deacon , "Thomas Gleixner" , Borislav Petkov , "H. Peter Anvin" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "Davidlohr Bueso" , Linus Torvalds , Tim Chen , huang ying Subject: RE: [PATCH-tip v7 08/20] locking/rwsem: Implement lock handoff to prevent lock starvation Thread-Topic: [PATCH-tip v7 08/20] locking/rwsem: Implement lock handoff to prevent lock starvation Thread-Index: AQHVAbGwED1ZCDfWWEWG7oek7uUiCKZZd8Ew Date: Fri, 3 May 2019 14:37:21 +0000 Message-ID: <62d8f603dc654d74b98cf2a5d4cf8c61@AcuMS.aculab.com> References: <20190428212557.13482-1-longman@redhat.com> <20190428212557.13482-9-longman@redhat.com> <20190503131054.GE2623@hirez.programming.kicks-ass.net> In-Reply-To: <20190503131054.GE2623@hirez.programming.kicks-ass.net> Accept-Language: en-GB, en-US Content-Language: 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 X-MC-Unique: sL2PkElbOGaMQnzoKPsUGw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peter Zijlstra > Sent: 03 May 2019 14:11 > To: Waiman Long ... > I've changed that like so. > > --- a/kernel/locking/rwsem.c > +++ b/kernel/locking/rwsem.c > @@ -406,19 +406,23 @@ static inline bool rwsem_try_write_lock( > long new; > > lockdep_assert_held(&sem->wait_lock); > + > do { > bool has_handoff = !!(count & RWSEM_FLAG_HANDOFF); > > if (has_handoff && wstate == WRITER_NOT_FIRST) > return false; > > + new = count; > + > if (count & RWSEM_LOCK_MASK) { > if (has_handoff || (wstate != WRITER_HANDOFF)) > return false; > - new = count | RWSEM_FLAG_HANDOFF; > + > + new |= RWSEM_FLAG_HANDOFF; > } else { > - new = (count | RWSEM_WRITER_LOCKED) & > - ~RWSEM_FLAG_HANDOFF; > + new |= RWSEM_WRITER_LOCKED; > + new &= ~RWSEM_FLAG_HANDOFF; > > if (list_is_singular(&sem->wait_list)) > new &= ~RWSEM_FLAG_WAITERS; The compiler will probably convert it back :-) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)