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 89F6DC04AB1 for ; Mon, 13 May 2019 09:13:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 635A921479 for ; Mon, 13 May 2019 09:13:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728645AbfEMJNb convert rfc822-to-8bit (ORCPT ); Mon, 13 May 2019 05:13:31 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:51352 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728619AbfEMJN3 (ORCPT ); Mon, 13 May 2019 05:13:29 -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-136-_UGF8YZbNt6WPKgejzV5ow-1; Mon, 13 May 2019 10:13:26 +0100 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; Mon, 13 May 2019 10:13:25 +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; Mon, 13 May 2019 10:13:25 +0100 From: David Laight To: 'Ingo Molnar' , Alexey Dobriyan CC: "linux-kernel@vger.kernel.org" , "x86@kernel.org" , Peter Zijlstra , Linus Torvalds , Thomas Gleixner , Borislav Petkov , Andy Lutomirski Subject: RE: FYI -ffreestanding shrinks kernel by 2% on x86_64 Thread-Topic: FYI -ffreestanding shrinks kernel by 2% on x86_64 Thread-Index: AQHVCWblbUBOOHnv10eqH+bQW22gjaZoxQGg Date: Mon, 13 May 2019 09:13:25 +0000 Message-ID: <3a3b9e840dbb456ab01815f7afdbb493@AcuMS.aculab.com> References: <20190511200223.GA14143@avx2> <20190511201344.GA11535@avx2> <20190512093228.GA8088@gmail.com> In-Reply-To: <20190512093228.GA8088@gmail.com> 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: _UGF8YZbNt6WPKgejzV5ow-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: Ingo Molnar > Sent: 12 May 2019 10:32 ... > Has anyone investigated by any chance where the -ffreestanding space > savings come from mostly - is it mostly in cold paths, or does it make or > hot codepaths more efficient as well? > > If it's the latter then the kernel would be directly faster as well > (fewer instructions executed), not just indirectly from better cache > packing, I suppse? My guess is that -ffreestanding stops gcc inlining memcpy() (etc). The calls can be smaller than the inline code, but will (probably) run more slowly. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)