Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752395AbYKKTQh (ORCPT ); Tue, 11 Nov 2008 14:16:37 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751437AbYKKTQ1 (ORCPT ); Tue, 11 Nov 2008 14:16:27 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:57152 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751297AbYKKTQ0 (ORCPT ); Tue, 11 Nov 2008 14:16:26 -0500 Date: Tue, 11 Nov 2008 19:13:55 +0000 From: Russell King To: Mathieu Desnoyers Cc: Nicolas Pitre , Andrew Morton , torvalds@linux-foundation.org, dhowells@redhat.com, mingo@elte.hu, a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org, ralf@linux-mips.org, benh@kernel.crashing.org, paulus@samba.org, davem@davemloft.net, mingo@redhat.com, tglx@linutronix.de, rostedt@goodmis.org, linux-arch@vger.kernel.org Subject: Re: [PATCH] convert cnt32_to_63 to inline Message-ID: <20081111191355.GA13724@flint.arm.linux.org.uk> Mail-Followup-To: Mathieu Desnoyers , Nicolas Pitre , Andrew Morton , torvalds@linux-foundation.org, dhowells@redhat.com, mingo@elte.hu, a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org, ralf@linux-mips.org, benh@kernel.crashing.org, paulus@samba.org, davem@davemloft.net, mingo@redhat.com, tglx@linutronix.de, rostedt@goodmis.org, linux-arch@vger.kernel.org References: <20081109162250.GB10181@Krystal> <20081109204256.89ab7925.akpm@linux-foundation.org> <20081110135850.0d620f3c.akpm@linux-foundation.org> <20081110152221.64948d23.akpm@linux-foundation.org> <20081111182759.GA8052@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081111182759.GA8052@Krystal> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2817 Lines: 73 On Tue, Nov 11, 2008 at 01:28:00PM -0500, Mathieu Desnoyers wrote: > Let's see what it gives once implemented. Only compile-tested. Assumes > pxa, sa110 and mn10300 are all UP-only. Correct smp_rmb() are used for > arm versatile. Versatile is also UP only. The following are results from PXA built with gcc 3.4.3: 1. two additional registers used in sched_clock() 2. 8 additional bytes of code (which are needless if gcc was more inteligent) both of these I put down to inefficiencies in gcc's register allocation. 3. worse instruction scheduling - two inter-dependent loads next to each other causing a pipeline stall Actual reading of variables/hardware is unaffected by this patch. Old code: c: e59f3050 ldr r3, [pc, #80] ; load address of oscr2ns_scale 10: e59fc050 ldr ip, [pc, #80] ; load address of __m_cnt_hi 14: e5932000 ldr r2, [r3] ; read oscr2ns_scale 18: e59f304c ldr r3, [pc, #76] ; load address of OSCR 1c: e59c1000 ldr r1, [ip] ; read __m_cnt_hi 20: e1a07002 mov r7, r2 24: e3a08000 mov r8, #0 ; 0x0 28: e5933000 ldr r3, [r3] ; read OSCR register ... 58: e1820b04 orr r0, r2, r4, lsl #22 5c: e1a01524 lsr r1, r4, #10 60: e89da9f0 ldm sp, {r4, r5, r6, r7, r8, fp, sp, pc} New code: c: e59f0058 ldr r0, [pc, #88] ; load address of oscr2ns_scale 10: e5901000 ldr r1, [r0] ; read oscr2ns_scale <= pipeline stall 14: e59f3054 ldr r3, [pc, #84] ; load address of __m_cnt_hi 18: e1a08001 mov r8, r1 1c: e5932000 ldr r2, [r3] ; read __m_cnt_hi 20: e59f304c ldr r3, [pc, #76] ; load address of OSCR 24: e1a09002 mov r9, r2 28: e3a0a000 mov sl, #0 ; 0x0 2c: e5933000 ldr r3, [r3] ; read OSCR ... 58: e1825b04 orr r5, r2, r4, lsl #22 5c: e1a06524 lsr r6, r4, #10 60: e1a01006 mov r1, r6 64: e1a00005 mov r0, r5 68: e89daff0 ldm sp, {r4, r5, r6, r7, r8, r9, sl, fp, sp, pc} Versatile: 1. 12 additional bytes of code 2. same number of registers 3. worse instruction scheduling causing pipeline stall Actual reading of variables/hardware is unaffected by this patch. So, we have two platforms where this patch makes things visibly worse with no material benefit. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: -- 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/