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 B3300C433EF for ; Fri, 18 Mar 2022 22:36:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241339AbiCRWiP convert rfc822-to-8bit (ORCPT ); Fri, 18 Mar 2022 18:38:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235601AbiCRWiM (ORCPT ); Fri, 18 Mar 2022 18:38:12 -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 6A55030DC4A for ; Fri, 18 Mar 2022 15:36:52 -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-218-9sJAWCXCNcmGyiXW6G-QUQ-1; Fri, 18 Mar 2022 22:36:48 +0000 X-MC-Unique: 9sJAWCXCNcmGyiXW6G-QUQ-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 15.0.1497.32; Fri, 18 Mar 2022 22:36:48 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.033; Fri, 18 Mar 2022 22:36:48 +0000 From: David Laight To: 'Segher Boessenkool' , Linus Torvalds CC: Andy Lutomirski , Andrew Cooper , Nick Desaulniers , "H. Peter Anvin" , Bill Wendling , "Thomas Gleixner" , Ingo Molnar , "Borislav Petkov" , Dave Hansen , "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" , "Nathan Chancellor" , Juergen Gross , "Peter Zijlstra" , "llvm@lists.linux.dev" , LKML , linux-toolchains Subject: RE: [PATCH v5] x86: use builtins to read eflags Thread-Topic: [PATCH v5] x86: use builtins to read eflags Thread-Index: AQHYOxW8eN2QBTsI8UeuD4rBr3nbhqzFuaDg Date: Fri, 18 Mar 2022 22:36:48 +0000 Message-ID: References: <83b33afc-8502-0065-60bc-3a91528632d8@kernel.org> <20220318220901.GS614@gate.crashing.org> In-Reply-To: <20220318220901.GS614@gate.crashing.org> 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: Segher Boessenkool > Sent: 18 March 2022 22:09 ... > It generally is a very good idea to > have a redzone though, without it you pay much more than necessary for > frame setup and teardown in leaf functions (similar to some of what the > misnamed "shrink-wrapping" optimisation does, but the two are mostly > independent, the benefits add up). Are there really leaf functions that need to spill data to stack where the cost of setting up a stack frame is significant? I'd have thought that was relatively rare. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)