Message-ID: <4DDA1973.4090309@pengutronix.de>
Date: Mon, 23 May 2011 10:23:15 +0200
From: Marc Kleine-Budde <mkl@pengutronix.de>
Organization: Pengutronix
User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Thunderbird/3.1.10
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To: Oliver Hartkopp <socketcan@hartkopp.net>
CC: Arnd Bergmann <arnd@arndb.de>,
        Subhasish Ghosh <subhasish@mistralsolutions.com>,
        Wolfgang Grandegger <wg@grandegger.com>, sachi@mistralsolutions.com,
        davinci-linux-open-source@linux.davincidsp.com, nsekhar@ti.com,
        open list <linux-kernel@vger.kernel.org>,
        CAN NETWORK DRIVERS <socketcan-core@lists.berlios.de>,
        linux-arm-kernel@lists.infradead.org, Netdev@vger.kernel.org,
        m-watkins@ti.com, Alan Cox <alan@lxorguk.ukuu.org.uk>
Subject: Re: [PATCH v4 1/1] can: add pruss CAN driver.
References: <1303474267-6344-1-git-send-email-subhasish@mistralsolutions.com> <4DCB88A4.2010901@grandegger.com> <4DCBF1B6.6000104@hartkopp.net> <201105221230.56243.arnd@arndb.de> <4DD9FCFC.10803@hartkopp.net>
In-Reply-To: <4DD9FCFC.10803@hartkopp.net>
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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 secon=
d (and
> therefore 21.000 irqs/s) - you are usually designing CAN network traffi=
c with
> less than 60% busload. So interrupt rates somewhere below 1000 irqs/s c=
an be
> assumed.
>=20
> From what i've seen so far a 3-4 messages rx FIFO and NAPI support just=
 make it.
>=20
> @Marc/Wolfgang: Would this be also your recommendation for a CAN contro=
ller
> 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
--=20
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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