linux-kernel - Re: [PATCH v4 1/1] can: add pruss CAN driver.

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Message-ID: <4DDA1973.4090309@pengutronix.de>
Date:	Mon, 23 May 2011 10:23:15 +0200
From:	Marc Kleine-Budde <mkl@...gutronix.de>
To:	Oliver Hartkopp <socketcan@...tkopp.net>
CC:	Arnd Bergmann <arnd@...db.de>,
	Subhasish Ghosh <subhasish@...tralsolutions.com>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	sachi@...tralsolutions.com,
	davinci-linux-open-source@...ux.davincidsp.com, nsekhar@...com,
	open list <linux-kernel@...r.kernel.org>,
	CAN NETWORK DRIVERS <socketcan-core@...ts.berlios.de>,
	linux-arm-kernel@...ts.infradead.org, Netdev@...r.kernel.org,
	m-watkins@...com, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v4 1/1] can: add pruss CAN driver.

On 05/23/2011 08:21 AM, Oliver Hartkopp wrote:

[...]

> In 'real world' CAN setups you'll never see 21.000 CAN frames per second (and
> therefore 21.000 irqs/s) - you are usually designing CAN network traffic with
> less than 60% busload. So interrupt rates somewhere below 1000 irqs/s can be
> assumed.
> 
> From what i've seen so far a 3-4 messages rx FIFO and NAPI support just make it.
> 
> @Marc/Wolfgang: Would this be also your recommendation for a CAN controller
> design that supports SocketCAN in the best way?

If you have a rx FIFO NAPI is the way to go. For a single mailbox it
adds overhead, if you can read the CAN frame in the interrupt handler.
The error messages should probably generated from NAPI, too. Especially
the I'm-the-only-CAN-node-on-the-net-and-get-no-ACK error message.

However IIRC David said that every new driver should implement NAPI.

> As the Linux network stack supports hardware timestamps too, this could be an
> additional (optional!) feature.

regards, Marc
-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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