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From: DENG Qingfang <dqfext@gmail.com>
To: Vladimir Oltean <olteanv@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
	Vladimir Oltean <vladimir.oltean@nxp.com>,
	netdev@vger.kernel.org, Jakub Kicinski <kuba@kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Kurt Kanzenbach <kurt@linutronix.de>,
	Woojung Huh <woojung.huh@microchip.com>,
	UNGLinuxDriver@microchip.com, Sean Wang <sean.wang@mediatek.com>,
	Landen Chao <Landen.Chao@mediatek.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Claudiu Manoil <claudiu.manoil@nxp.com>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
	George McCollister <george.mccollister@gmail.com>
Subject: Re: [RFC PATCH net-next 2/4] net: dsa: remove the "dsa_to_port in a loop" antipattern from the core
Date: Wed, 11 Aug 2021 01:04:47 +0800	[thread overview]
Message-ID: <20210810170447.1517888-1-dqfext@gmail.com> (raw)
In-Reply-To: <20210810163533.bn7zq2dzcilfm6o5@skbuf>

On Tue, Aug 10, 2021 at 07:35:33PM +0300, Vladimir Oltean wrote:
> If I were to guess where Qingfang was hinting at, is that the receive
> path now needs to iterate over a list, whereas before it simply indexed
> an array:
> 
> static inline struct net_device *dsa_master_find_slave(struct net_device *dev,
> 						       int device, int port)
> {
> 	struct dsa_port *cpu_dp = dev->dsa_ptr;
> 	struct dsa_switch_tree *dst = cpu_dp->dst;
> 	struct dsa_port *dp;
> 
> 	list_for_each_entry(dp, &dst->ports, list)
> 		if (dp->ds->index == device && dp->index == port &&
> 		    dp->type == DSA_PORT_TYPE_USER)
> 			return dp->slave;
> 
> 	return NULL;
> }
> 
> I will try in the following days to make a prototype implementation of
> converting back the linked list into an array and see if there is any
> justifiable performance improvement.
> 
> [ even if this would make the "multiple CPU ports in LAG" implementation
>   harder ]

Yes, you got my point.

There is RTL8390M series SoC, which has 52+ ports but a weak CPU (MIPS
34kc 700MHz). In that case the linear lookup time and the potential cache
miss could make a difference.

  reply	other threads:[~2021-08-10 17:05 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09 19:03 [RFC PATCH net-next 0/4] Remove the "dsa_to_port in a loop" antipattern Vladimir Oltean
2021-08-09 19:03 ` [RFC PATCH net-next 1/4] net: dsa: introduce a dsa_port_is_unused helper Vladimir Oltean
2021-08-10  9:34   ` Florian Fainelli
2021-08-09 19:03 ` [RFC PATCH net-next 2/4] net: dsa: remove the "dsa_to_port in a loop" antipattern from the core Vladimir Oltean
2021-08-10  3:33   ` DENG Qingfang
2021-08-10  9:41     ` Florian Fainelli
2021-08-10 11:35       ` Vladimir Oltean
2021-08-10 16:35         ` Vladimir Oltean
2021-08-10 17:04           ` DENG Qingfang [this message]
2021-08-11 17:32             ` Vladimir Oltean
2021-08-10  9:37   ` Florian Fainelli
2021-08-09 19:03 ` [RFC PATCH net-next 3/4] net: dsa: remove the "dsa_to_port in a loop" antipattern from drivers Vladimir Oltean
2021-08-09 19:03 ` [RFC PATCH net-next 4/4] net: dsa: b53: express b53_for_each_port in terms of dsa_switch_for_each_port Vladimir Oltean
2021-08-10  9:39   ` Florian Fainelli
2021-08-10 13:14     ` Vladimir Oltean
2021-08-09 19:31 ` [RFC PATCH net-next 0/4] Remove the "dsa_to_port in a loop" antipattern Vladimir Oltean

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