From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5DDD9C77B72 for ; Mon, 17 Apr 2023 07:26:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230218AbjDQH0n (ORCPT ); Mon, 17 Apr 2023 03:26:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230211AbjDQH0i (ORCPT ); Mon, 17 Apr 2023 03:26:38 -0400 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A72C940F5 for ; Mon, 17 Apr 2023 00:26:30 -0700 (PDT) Received: from moin.white.stw.pengutronix.de ([2a0a:edc0:0:b01:1d::7b] helo=bjornoya.blackshift.org) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1poJFh-0006hA-8x; Mon, 17 Apr 2023 09:26:17 +0200 Received: from pengutronix.de (unknown [172.20.34.65]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) (Authenticated sender: mkl-all@blackshift.org) by smtp.blackshift.org (Postfix) with ESMTPSA id 0A8271B04D6; Mon, 17 Apr 2023 07:26:14 +0000 (UTC) Date: Mon, 17 Apr 2023 09:26:13 +0200 From: Marc Kleine-Budde To: Oliver Hartkopp Cc: Judith Mendez , Chandrasekar Ramakrishnan , Nishanth Menon , Vignesh Raghavendra , Andrew Davis , Wolfgang Grandegger , Rob Herring , Krzysztof Kozlowski , linux-can@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, netdev@vger.kernel.org, Schuyler Patton Subject: Re: [RFC PATCH 5/5] can: m_can: Add hrtimer to generate software interrupt Message-ID: <20230417-taking-relieving-f2c8532864c0-mkl@pengutronix.de> References: <20230413223051.24455-1-jm@ti.com> <20230413223051.24455-6-jm@ti.com> <20230414-bounding-guidance-262dffacd05c-mkl@pengutronix.de> <4a6c66eb-2ccf-fc42-a6fc-9f411861fcef@hartkopp.net> <20230416-failing-washbasin-e4fa5caea267-mkl@pengutronix.de> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="f6bxkwneko5oxwq5" Content-Disposition: inline In-Reply-To: X-SA-Exim-Connect-IP: 2a0a:edc0:0:b01:1d::7b X-SA-Exim-Mail-From: mkl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: devicetree@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org --f6bxkwneko5oxwq5 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 16.04.2023 21:46:40, Oliver Hartkopp wrote: > > I had the 5ms that are actually used in the code in mind. But this is a > > good calculation. >=20 > @Judith: Can you acknowledge the value calculation? >=20 > > > The "shortest" 11 bit CAN ID CAN frame is a Classical CAN frame with = DLC =3D 0 > > > and 1 Mbit/s (arbitration) bitrate. This should be 48 bits @1Mbit =3D= > ~50 > > > usecs > > >=20 > > > So it should be something about > > >=20 > > > 50 usecs * (FIFO queue len - 2) > >=20 > > Where does the "2" come from? >=20 > I thought about handling the FIFO earlier than it gets completely "full". >=20 > The fetching routine would need some time too and the hrtimer could also > jitter to some extend. I was assuming something like this. I would argue that the polling time should be: 50 =C2=B5s * FIFO length - IRQ overhead. The max IRQ overhead depends on your SoC and kernel configuration. regards, Marc --=20 Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung N=C3=BCrnberg | Phone: +49-5121-206917-129 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 | --f6bxkwneko5oxwq5 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAABCgAdFiEEDs2BvajyNKlf9TJQvlAcSiqKBOgFAmQ89JIACgkQvlAcSiqK BOj1QAf8C3XM8k07BC2j8JyiAa7udtivyxZJ8HO2LKeVF312gm8khfUIMOo06Sqp jW+3LndAnjaby9ahmfPCWHwPPdF6X1xWJhH+JUCFTeM6C7JBdtKjSkFcVx2o69ot ZgMQnqOaxunKcnm2EOTOSsP9P2PLNzjm0MD0Nf+soV9PYgMdLfl/oKjZRMqQFbG/ yMMZ40JaMt9kzwZSE9d6YE/EfygUmHmYQERz3OXGMhKVLMEe0CrOOKV+goEXvJfP SOg+kCqU14RzDC8fzJMk8Ju1bgICmQksIvHAH05hbuCctWjhePYHINx3kF8JZut+ yJP8lWEBWlsf+uGi7oINsvn6ZTY4WA== =3slR -----END PGP SIGNATURE----- --f6bxkwneko5oxwq5--