From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964849AbWAKVOF (ORCPT ); Wed, 11 Jan 2006 16:14:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964854AbWAKVOF (ORCPT ); Wed, 11 Jan 2006 16:14:05 -0500 Received: from smtp-103-wednesday.noc.nerim.net ([62.4.17.103]:34832 "EHLO mallaury.nerim.net") by vger.kernel.org with ESMTP id S964849AbWAKVOD (ORCPT ); Wed, 11 Jan 2006 16:14:03 -0500 Date: Wed, 11 Jan 2006 22:14:12 +0100 From: Jean Delvare To: LKML Subject: [RFC] copy loop versus memcpy Message-Id: <20060111221412.57ef8fc1.khali@linux-fr.org> X-Mailer: Sylpheed version 2.0.4 (GTK+ 2.6.10; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi all, I am considering applying the following patch, in the hope to slightly speed up some I2C/SMBus transfers. Am I right assuming that using memcpy is faster than an explicit copy loop? The typical data size will be 32 bytes. Thanks. --- drivers/i2c/i2c-core.c | 15 ++++++--------- 1 file changed, 6 insertions(+), 9 deletions(-) --- linux-2.6.15-git.orig/drivers/i2c/i2c-core.c 2006-01-11 18:53:43.000000000 +0100 +++ linux-2.6.15-git/drivers/i2c/i2c-core.c 2006-01-11 21:35:53.000000000 +0100 @@ -921,12 +921,11 @@ u8 length, u8 *values) { union i2c_smbus_data data; - int i; + if (length > I2C_SMBUS_BLOCK_MAX) length = I2C_SMBUS_BLOCK_MAX; - for (i = 1; i <= length; i++) - data.block[i] = values[i-1]; data.block[0] = length; + memcpy(data.block + 1, values, length); return i2c_smbus_xfer(client->adapter,client->addr,client->flags, I2C_SMBUS_WRITE,command, I2C_SMBUS_BLOCK_DATA,&data); @@ -936,16 +935,14 @@ s32 i2c_smbus_read_i2c_block_data(struct i2c_client *client, u8 command, u8 *values) { union i2c_smbus_data data; - int i; + if (i2c_smbus_xfer(client->adapter,client->addr,client->flags, I2C_SMBUS_READ,command, I2C_SMBUS_I2C_BLOCK_DATA,&data)) return -1; - else { - for (i = 1; i <= data.block[0]; i++) - values[i-1] = data.block[i]; - return data.block[0]; - } + + memcpy(values, data.block + 1, data.block[0]); + return data.block[0]; } s32 i2c_smbus_write_i2c_block_data(struct i2c_client *client, u8 command, -- Jean Delvare