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=-0.8 required=3.0 tests=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 003E7C3F2D6 for ; Fri, 6 Mar 2020 16:58:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D70D22166E for ; Fri, 6 Mar 2020 16:57:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726462AbgCFQ57 convert rfc822-to-8bit (ORCPT ); Fri, 6 Mar 2020 11:57:59 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:57193 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725935AbgCFQ57 (ORCPT ); Fri, 6 Mar 2020 11:57:59 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-20-vOmmemdGMmSebKCtFim0sQ-1; Fri, 06 Mar 2020 16:57:55 +0000 X-MC-Unique: vOmmemdGMmSebKCtFim0sQ-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, 6 Mar 2020 16:57:55 +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, 6 Mar 2020 16:57:55 +0000 From: David Laight To: 'Peter Zijlstra' , =?iso-8859-1?Q?Andr=E9_Almeida?= CC: Florian Weimer , "Pierre-Loup A. Griffais" , Thomas Gleixner , "linux-kernel@vger.kernel.org" , "kernel@collabora.com" , "krisman@collabora.com" , "shuah@kernel.org" , "linux-kselftest@vger.kernel.org" , "rostedt@goodmis.org" , "ryao@gentoo.org" , "dvhart@infradead.org" , "mingo@redhat.com" , "z.figura12@gmail.com" , "steven@valvesoftware.com" , "steven@liquorix.net" , "malteskarupke@web.de" , "carlos@redhat.com" , "adhemerval.zanella@linaro.org" , "libc-alpha@sourceware.org" , "linux-api@vger.kernel.org" Subject: RE: 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes] Thread-Topic: 'simple' futex interface [Was: [PATCH v3 1/4] futex: Implement mechanism to wait on any of several futexes] Thread-Index: AQHV8x8l7LKRap7vfU2BMMqcavNvO6g7ya9A Date: Fri, 6 Mar 2020 16:57:54 +0000 Message-ID: <0271e473ddcf463bb030eb4cbecbe888@AcuMS.aculab.com> References: <87tv3aflqm.fsf@nanos.tec.linutronix.de> <967d5047-2cb6-d6d8-6107-edb99a4c9696@valvesoftware.com> <87o8thg031.fsf@nanos.tec.linutronix.de> <20200303120050.GC2596@hirez.programming.kicks-ass.net> <87pndth9ur.fsf@oldenburg2.str.redhat.com> <20200303132150.GD2596@hirez.programming.kicks-ass.net> <878skhh7og.fsf@oldenburg2.str.redhat.com> <20200303150104.GE2596@hirez.programming.kicks-ass.net> <52406c54-60b3-dcfe-65d8-4c425459e37b@collabora.com> <20200305185136.GB3348@worktop.programming.kicks-ass.net> In-Reply-To: <20200305185136.GB3348@worktop.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-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org From: Peter Zijlstra > Sent: 05 March 2020 18:52 +> On Thu, Mar 05, 2020 at 01:14:17PM -0300, André Almeida wrote: > > > > sys_futex_wait(void *uaddr, u64 val, unsigned long flags, ktime_t *timo); > > > struct futex_wait { > > > void *uaddr; > > > u64 val; > > > u64 flags; > > > }; > > > sys_futex_waitv(struct futex_wait *waiters, unsigned int nr_waiters, > > > u64 flags, ktime_t *timo); > > > sys_futex_wake(void *uaddr, unsigned int nr, u64 flags); > > > sys_futex_cmp_requeue(void *uaddr1, void *uaddr2, unsigned int nr_wake, > > > unsigned int nr_requeue, u64 cmpval, unsigned long flags); > > > > > > And that makes 7 arguments for cmp_requeue, which can't be. Maybe we if > > > combine nr_wake and nr_requeue in one as 2 u16... ? > > > > > > And then we need to go detector if the platform supports it or not.. > > > > > > > Thanks everyone for the feedback around our mechanism. Are the > > performance benefits of implementing a syscall to wait on a single futex > > significant enough to maintain it instead of just using > > `sys_futex_waitv()` with `nr_waiters = 1`? If we join both cases in a > > single interface, we may even add a new member for NUMA hint in `struct > > futex_wait`. > > My consideration was that avoiding the get_user/copy_from_user might > become measurable on !PTI systems with SMAP. > > But someone would have to build it and measure it before we can be sure > of course. An extra copy_from_user is likely to be noticable. It certainly makes recvmsg() slower than recv(). Especially if the hardended usercopy crap gets involved. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)