From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Laight Subject: RE: [PATCH 04/18] csum_and_copy_..._user(): pass 0xffffffff instead of 0 as initial sum Date: Thu, 23 Jul 2020 15:36:52 +0000 Message-ID: <1ba695b2264349f187f825ff2c308624@AcuMS.aculab.com> References: <20200721202549.4150745-1-viro@ZenIV.linux.org.uk> <20200721202549.4150745-4-viro@ZenIV.linux.org.uk> <2d85ebb8ea2248c8a14f038a0c60297e@AcuMS.aculab.com> <20200722144213.GE2786714@ZenIV.linux.org.uk> <4e03cce8ed184d40bb0ea40fd3d51000@AcuMS.aculab.com> <20200722155452.GF2786714@ZenIV.linux.org.uk> <20200722173903.GG2786714@ZenIV.linux.org.uk> <02938acd78fd40beb02ffc5a1b803d85@AcuMS.aculab.com> <20200723145342.GH2786714@ZenIV.linux.org.uk> <20200723152101.GI2786714@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Return-path: Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:56583 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726761AbgGWPg5 (ORCPT ); Thu, 23 Jul 2020 11:36:57 -0400 In-Reply-To: <20200723152101.GI2786714@ZenIV.linux.org.uk> Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org List-ID: To: 'Al Viro' Cc: Linus Torvalds , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" From: Al Viro > Sent: 23 July 2020 16:21 ... > The point is, your "~4.5 cycles per vector" is pretty much noise and the > difference between the 3-argument and 4-argument variants could easily be > in the same range. It might be a valid microoptimization, it might be not. > 3-argument variant is simpler and IMO in absence of strong data we ought > to go with that. There is definitely more to be gained by rewriting the x86-86 asm. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)