[RFC] copy loop versus memcpy

[Jean Delvare <khali@linux-fr.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