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Tue, 22 Oct 2019 12:49:08 -0400 Received: from gallifrey.ext.pengutronix.de ([2001:67c:670:201:5054:ff:fe8d:eefb] 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 1iMxLE-00054w-PJ; Tue, 22 Oct 2019 18:49:04 +0200 Received: from [IPv6:2a03:f580:87bc:d400:dcd0:3ded:5374:df72] (unknown [IPv6:2a03:f580:87bc:d400:dcd0:3ded:5374:df72]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits)) (Client CN "mkl@blackshift.org", Issuer "StartCom Class 1 Client CA" (not verified)) (Authenticated sender: mkl@blackshift.org) by smtp.blackshift.org (Postfix) with ESMTPSA id 1C82B46CBC1; Tue, 22 Oct 2019 16:49:01 +0000 (UTC) To: Stephen Hemminger Cc: Vincent Prince , jiri@resnulli.us, jhs@mojatatu.com, netdev@vger.kernel.org, dave.taht@gmail.com, linux-can@vger.kernel.org, kernel@pengutronix.de, xiyou.wangcong@gmail.com, davem@davemloft.net References: <20190327165632.10711-1-mkl@pengutronix.de> <1571750597-14030-1-git-send-email-vincent.prince.fr@gmail.com> <84b8ce24-fe5d-ead0-0d1d-03ea24b36f71@pengutronix.de> <20191022094254.489fd6a4@hermes.lan> From: Marc Kleine-Budde Openpgp: preference=signencrypt Autocrypt: addr=mkl@pengutronix.de; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20191022094254.489fd6a4@hermes.lan> Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="ZGX4thhKU5ySb8F1SQIYPsBtz9A5sBeYZ" X-SA-Exim-Connect-IP: 2001:67c:670:201:5054:ff:fe8d:eefb 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: netdev@vger.kernel.org Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --ZGX4thhKU5ySb8F1SQIYPsBtz9A5sBeYZ Content-Type: multipart/mixed; boundary="cJsv4zNEKbGVh1R1bCCefmlaO90Kd3gsf"; protected-headers="v1" From: Marc Kleine-Budde To: Stephen Hemminger Cc: Vincent Prince , jiri@resnulli.us, jhs@mojatatu.com, netdev@vger.kernel.org, dave.taht@gmail.com, linux-can@vger.kernel.org, kernel@pengutronix.de, xiyou.wangcong@gmail.com, davem@davemloft.net Message-ID: Subject: Re: [PATCH v2] net: sch_generic: Use pfifo_fast as fallback scheduler for CAN hardware References: <20190327165632.10711-1-mkl@pengutronix.de> <1571750597-14030-1-git-send-email-vincent.prince.fr@gmail.com> <84b8ce24-fe5d-ead0-0d1d-03ea24b36f71@pengutronix.de> <20191022094254.489fd6a4@hermes.lan> In-Reply-To: <20191022094254.489fd6a4@hermes.lan> --cJsv4zNEKbGVh1R1bCCefmlaO90Kd3gsf Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: quoted-printable On 10/22/19 6:42 PM, Stephen Hemminger wrote: > On Tue, 22 Oct 2019 16:53:44 +0200 > Marc Kleine-Budde wrote: >=20 >> On 10/22/19 3:23 PM, Vincent Prince wrote: >>> Signed-off-by: Vincent Prince =20 >> >> please include a patch description. I.e. this one: >> >> -------->8-------->8-------->8-------->8-------->8-------->8-------->8= -------- =20 >> There is networking hardware that isn't based on Ethernet for layers 1= and 2. >> >> For example CAN. >> >> CAN is a multi-master serial bus standard for connecting Electronic Co= ntrol >> Units [ECUs] also known as nodes. A frame on the CAN bus carries up to= 8 bytes >> of payload. Frame corruption is detected by a CRC. However frame loss = due to >> corruption is possible, but a quite unusual phenomenon. >> >> While fq_codel works great for TCP/IP, it doesn't for CAN. There are a= lot of >> legacy protocols on top of CAN, which are not build with flow control = or high >> CAN frame drop rates in mind. >> >> When using fq_codel, as soon as the queue reaches a certain delay base= d length, >> skbs from the head of the queue are silently dropped. Silently meaning= that the ^^^^^^^^^^^^^^^^^ >> user space using a send() or similar syscall doesn't get an error. How= ever >> TCP's flow control algorithm will detect dropped packages and adjust t= he >> bandwidth accordingly. > Why not fix fq_codel to return the same errors as other qdisc? The head drop is the problem. After a send() system call returned to user space, one would not expect that a later send() will knock an earlier from the queue. It's too late to throttle the package generation, as one frame is lost already. 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 | --cJsv4zNEKbGVh1R1bCCefmlaO90Kd3gsf-- --ZGX4thhKU5ySb8F1SQIYPsBtz9A5sBeYZ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEmvEkXzgOfc881GuFWsYho5HknSAFAl2vMvgACgkQWsYho5Hk nSAzwggApHPLYwEg78qvJeyYoQ7Q6601g0Yulhyz3CLoAwyTMppHNesegAYMpfFZ D+8kMjLi9x2BhRMBujQYNOP9A82JirEYdiPBoTheqWWF1juEU01Z9UrKKRuKHn9A F1hVrh1EcobK5ymr4+wrsl+XSnmz3V8+ytp+skFVQcjofv0qsTzmK57fTlHe/Hfo UFhzRsfOw3dksOCQ0vrKy7a491tE68ecLJz6VxmTIZI3CcJeb2UhZqqvTGVSw7fQ MqyvNgym2Evqvis8Tf2ih298KOvx8GCw/twgcMD9qCc3RaWgdWlZu2mOIJuhxUph gj6IiYRYHCGVcgLX/hhtf85HMAbhxA== =DERk -----END PGP SIGNATURE----- --ZGX4thhKU5ySb8F1SQIYPsBtz9A5sBeYZ--