netdev - Re: [net-next PATCH v3 01/14] net: dsa: qca8k: cache match data to speed up access

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Date:   Mon, 25 Jul 2022 01:30:31 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Christian Marangi <ansuelsmth@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [net-next PATCH v3 01/14] net: dsa: qca8k: cache match data to
 speed up access

On Sat, Jul 23, 2022 at 04:18:32PM +0200, Christian Marangi wrote:
> Using of_device_get_match_data is expensive. Cache match data to speed

'is expensive' sounds like it's terribly expensive. It's just more than
it needs to be.

> up access and rework user of match data to use the new cached value.
> 
> Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
> ---
>  drivers/net/dsa/qca/qca8k.c | 28 ++++++++++------------------
>  drivers/net/dsa/qca/qca8k.h |  1 +
>  2 files changed, 11 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/net/dsa/qca/qca8k.c b/drivers/net/dsa/qca/qca8k.c
> index 1cbb05b0323f..212b284f9f73 100644
> --- a/drivers/net/dsa/qca/qca8k.c
> +++ b/drivers/net/dsa/qca/qca8k.c
> @@ -3168,6 +3155,11 @@ qca8k_sw_probe(struct mdio_device *mdiodev)
>  	if (ret)
>  		return ret;
>  
> +	/* Cache match data in priv struct.
> +	 * Match data is already checked in read_switch_id.
> +	 */
> +	priv->info = of_device_get_match_data(priv->dev);
> +

So why don't you set priv->info right before calling qca8k_read_switch_id(),
then?

>  	priv->ds = devm_kzalloc(&mdiodev->dev, sizeof(*priv->ds), GFP_KERNEL);
>  	if (!priv->ds)
>  		return -ENOMEM;
> diff --git a/drivers/net/dsa/qca/qca8k.h b/drivers/net/dsa/qca/qca8k.h
> index ec58d0e80a70..0b990b46890a 100644
> --- a/drivers/net/dsa/qca/qca8k.h
> +++ b/drivers/net/dsa/qca/qca8k.h
> @@ -401,6 +401,7 @@ struct qca8k_priv {
>  	struct qca8k_mdio_cache mdio_cache;
>  	struct qca8k_pcs pcs_port_0;
>  	struct qca8k_pcs pcs_port_6;
> +	const struct qca8k_match_data *info;
>  };
>  
>  struct qca8k_mib_desc {
> -- 
> 2.36.1
>