Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932120AbVJCC4U (ORCPT ); Sun, 2 Oct 2005 22:56:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932122AbVJCC4U (ORCPT ); Sun, 2 Oct 2005 22:56:20 -0400 Received: from h80ad24a6.async.vt.edu ([128.173.36.166]:31877 "EHLO h80ad24a6.async.vt.edu") by vger.kernel.org with ESMTP id S932120AbVJCC4T (ORCPT ); Sun, 2 Oct 2005 22:56:19 -0400 Message-Id: <200510030255.j932toIK012248@turing-police.cc.vt.edu> X-Mailer: exmh version 2.7.2 01/07/2005 with nmh-1.1-RC3 To: Luke Kenneth Casson Leighton Cc: Vadim Lobanov , Rik van Riel , linux-kernel@vger.kernel.org Subject: Re: what's next for the linux kernel? In-Reply-To: Your message of "Mon, 03 Oct 2005 01:54:00 BST." <20051003005400.GM6290@lkcl.net> From: Valdis.Kletnieks@vt.edu References: <20051002204703.GG6290@lkcl.net> <20051002230545.GI6290@lkcl.net> <20051003005400.GM6290@lkcl.net> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="==_Exmh_1128308149_12821P"; micalg=pgp-sha1; protocol="application/pgp-signature" Content-Transfer-Encoding: 7bit Date: Sun, 02 Oct 2005 22:55:49 -0400 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2107 Lines: 49 --==_Exmh_1128308149_12821P Content-Type: text/plain; charset=us-ascii On Mon, 03 Oct 2005 01:54:00 BST, Luke Kenneth Casson Leighton said: > in the mid-80s), hardware cache line lookups (which means > instead of linked list searching, the hardware does it for > you in a single cycle), stuff like that. OK.. I'll bite. How do you find the 5th or 6th entry in the linked list, when only the first entry is in cache, in a single cycle, when a cache line miss is more than a single cycle penalty, and you have several "These are not the droids you're looking for" checks and go on to the next entry - and do it in one clock cycle? Now, it's really easy to imagine an execution unit that will execute this as a single opcode, and stall until complete. Of course, this only really helps if you have multiple execution units - which is what hyperthreading and multi-core and all that is about. And guess what - it's not news... The HP2114 and DEC KL10/20 were able to dereference a chain of indirect bits back in the 70's (complete with warnings that hardware wedges could occur if an indirect reference formed a loop or pointed at itself). Whoops. :) And all the way back in 1964, IBM disk controllers were able to do some rather sophisticated offloading of "channel control words" (amazing what you could do with 'Search ID Equal', 'Transfer In-Channel' (really a misnamed branch instruction), and self-modifying CCWs). But even then, they understood that it was only a win if you could go do other stuff when you waited.... --==_Exmh_1128308149_12821P Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2 (GNU/Linux) Comment: Exmh version 2.5 07/13/2001 iD8DBQFDQJ21cC3lWbTT17ARApo8AKDZlVwCkCSCz9pKtU84tU/JeJr8ZQCeInwD WVR/tiTrZRtxNjd+qzz/liw= =tjuo -----END PGP SIGNATURE----- --==_Exmh_1128308149_12821P-- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/