Re: [PATCH v4 1/1] can: add pruss CAN driver. - Marc Kleine-Budde

From: Marc Kleine-Budde <mkl-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
To: Oliver Hartkopp <socketcan-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>
Cc: sachi-EvXpCiN+lbve9wHmmfpqLFaTQe2KTcn/@public.gmane.org,
	davinci-linux-open-source-VycZQUHpC/PFrsHnngEfi1aTQe2KTcn/@public.gmane.org,
	Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>,
	Subhasish Ghosh
	<subhasish-EvXpCiN+lbve9wHmmfpqLFaTQe2KTcn/@public.gmane.org>,
	nsekhar-l0cyMroinI0@public.gmane.org,
	open list <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	CAN NETWORK DRIVERS
	<socketcan-core-0fE9KPoRgkgATYTw5x5z8w@public.gmane.org>,
	Alan Cox <alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	Netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	m-watkins-l0cyMroinI0@public.gmane.org,
	Wolfgang Grandegger <wg-5Yr1BZd7O62+XT7JhA+gdA@public.gmane.org>
Subject: Re: [PATCH v4 1/1] can: add pruss CAN driver.
Date: Mon, 23 May 2011 10:23:15 +0200	[thread overview]
Message-ID: <4DDA1973.4090309@pengutronix.de> (raw)
In-Reply-To: <4DD9FCFC.10803-fJ+pQTUTwRTk1uMJSBkQmQ@public.gmane.org>

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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     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |

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