linux-kernel - Re: [PATCH] can: c_can: Speed up rx

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Message-ID: <1382980336.30941.40.camel@joe-AO722>
Date:	Mon, 28 Oct 2013 10:12:16 -0700
From:	Joe Perches <joe@...ches.com>
To:	Markus Pargmann <mpa@...gutronix.de>
Cc:	Marc Kleine-Budde <mkl@...gutronix.de>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	linux-can@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH] can: c_can: Speed up rx_poll function

On Mon, 2013-10-28 at 17:59 +0100, Markus Pargmann wrote:
> This patch speeds up the rx_poll function by reducing the number of
> register reads.

trivial notes:

> diff --git a/drivers/net/can/c_can/c_can.c b/drivers/net/can/c_can/c_can.c
[]
> @@ -259,6 +259,12 @@ static u32 c_can_read_reg32(struct c_can_priv *priv, enum reg index)
> +u16 c_can_read_reg16(struct c_can_priv *priv, enum reg index)
> +{
> +	u16 val = priv->read_reg(priv, index);
> +	return val;
> +}

This function doesn't seem useful at all.
It's not exported and it's not static.

Why not use an in-place priv->read_reg(priv, index)?

> +
>  static void c_can_enable_all_interrupts(struct c_can_priv *priv,
>  						int enable)
>  {
> @@ -798,17 +804,21 @@ static int c_can_do_rx_poll(struct net_device *dev, int quota)
>  	u32 num_rx_pkts = 0;
>  	unsigned int msg_obj, msg_ctrl_save;
>  	struct c_can_priv *priv = netdev_priv(dev);
> -	u32 val = c_can_read_reg32(priv, C_CAN_INTPND1_REG);
> +	unsigned long val = c_can_read_reg16(priv, C_CAN_INTPND1_REG);

Probably better as a u16 as detailed below.

> +	/*
> +	 * It is faster to read only one 16bit register. This is only possible
> +	 * for a maximum number of 16 objects.
> +	 */
> +	BUILD_BUG_ON_MSG(C_CAN_MSG_OBJ_RX_LAST > 16,
> +			"Implementation does not support more message objects than 16");
> +
> +	while (quota > 0 && (val = c_can_read_reg16(priv, C_CAN_INTPND1_REG))) {
> +		msg_obj = 0;
> +		while ((msg_obj = find_next_bit(&val, 16, msg_obj)) < 16 &&

Using ffs instead of find_next_bit would be more standard
and probably faster too.


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