Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757968Ab3CNPHA (ORCPT ); Thu, 14 Mar 2013 11:07:00 -0400 Received: from mail-lb0-f181.google.com ([209.85.217.181]:56384 "EHLO mail-lb0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756894Ab3CNPG6 (ORCPT ); Thu, 14 Mar 2013 11:06:58 -0400 MIME-Version: 1.0 Date: Thu, 14 Mar 2013 23:06:56 +0800 Message-ID: Subject: In SMP, every CPU has its own loops_per_jiffy value, __loop_const_udelay time period is not right if two cpus are running in different frequency. From: chpoph To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1907 Lines: 80 in __loop_const_udelay function, the delayed time period is calculated according to loops_per_jiffy. In SMP, every CPU has its own loops_per_jiffy value, __loop_const_udelay time period is not right if two cpus are running in different frequency. the following is file arch/arm/lib/delay-loop.S /* * linux/arch/arm/lib/delay.S * * Copyright (C) 1995, 1996 Russell King * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. */ #include #include #include .text .LC0: .word loops_per_jiffy .LC1: .word UDELAY_MULT /* * r0 <= 2000 * lpj <= 0x01ffffff (max. 3355 bogomips) * HZ <= 1000 */ ENTRY(__loop_udelay) ldr r2, .LC1 mul r0, r2, r0 ENTRY(__loop_const_udelay) @ 0 <= r0 <= 0x7fffff06 mov r1, #-1 ldr r2, .LC0 ldr r2, [r2] @ max = 0x01ffffff add r0, r0, r1, lsr #32-14 mov r0, r0, lsr #14 @ max = 0x0001ffff add r2, r2, r1, lsr #32-10 mov r2, r2, lsr #10 @ max = 0x00007fff mul r0, r2, r0 @ max = 2^32-1 add r0, r0, r1, lsr #32-6 movs r0, r0, lsr #6 moveq pc, lr /* * loops = r0 * HZ * loops_per_jiffy / 1000000 */ @ Delay routine ENTRY(__loop_delay) subs r0, r0, #1 #if 0 movls pc, lr subs r0, r0, #1 movls pc, lr subs r0, r0, #1 movls pc, lr subs r0, r0, #1 movls pc, lr subs r0, r0, #1 movls pc, lr subs r0, r0, #1 movls pc, lr subs r0, r0, #1 movls pc, lr subs r0, r0, #1 #endif bhi __loop_delay mov pc, lr ENDPROC(__loop_udelay) ENDPROC(__loop_const_udelay) ENDPROC(__loop_delay) -- 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/