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From: David Laight <David.Laight@ACULAB.COM>
To: 'Florian Fainelli' <f.fainelli@gmail.com>,
	Vladimir Oltean <vladimir.oltean@nxp.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Cc: "andrew@lunn.ch" <andrew@lunn.ch>,
	"vivien.didelot@gmail.com" <vivien.didelot@gmail.com>,
	"kuba@kernel.org" <kuba@kernel.org>,
	"Christian Eggers" <ceggers@arri.de>,
	Kurt Kanzenbach <kurt@linutronix.de>
Subject: RE: [RFC PATCH 02/13] net: dsa: implement a central TX reallocation procedure
Date: Mon, 19 Oct 2020 08:33:27 +0000
Message-ID: <049e7fd8f46c43819a05689fe464df25@AcuMS.aculab.com> (raw)
In-Reply-To: <d2578c4b-7da6-e25d-5dde-5ec89b82aeef@gmail.com>

From: Florian Fainelli>
> Sent: 17 October 2020 23:12
..
> Not positive you need that because you may be account for more head or
> tail room than necessary.
> 
> For instance with tag_brcm.c and systemport.c we need 4 bytes of head
> room for the Broadcom tag and an additional 8 bytes for pushing the
> transmit status block descriptor in front of the Ethernet frame about to
> be transmitted. These additional 8 bytes are a requirement of the DSA
> master here and exist regardless of DSA being used, but we should not be
> propagating them to the DSA slave.

Is it possible to send the extra bytes from a separate buffer fragment?
The entire area could be allocated (coherent) when the rings are
allocated.
That would save having to modify the skb at all.

Even if some bytes of the frame header need 'adjusting' transmitting
from a copy may be faster - especially on systems with an iommu.

Many (many) moons ago we found the cutoff point for copying frames
on a system with an iommu to be around 1k bytes.

	David

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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

  parent reply index

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-17 21:35 [RFC PATCH 00/13] Generic TX reallocation for DSA Vladimir Oltean
2020-10-17 21:35 ` [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev statistics Vladimir Oltean
2020-10-17 22:13   ` Florian Fainelli
2020-10-17 23:15   ` Andrew Lunn
2020-10-18  0:23     ` Vladimir Oltean
2020-10-18 12:02   ` Heiner Kallweit
2020-10-18 12:16     ` Vladimir Oltean
2020-10-18 13:09       ` Heiner Kallweit
2020-10-18 13:48         ` Vladimir Oltean
2020-10-18 14:13           ` Heiner Kallweit
2020-10-18 22:58             ` Vladimir Oltean
2020-10-18 23:11               ` Florian Fainelli
2020-10-19  0:21                 ` Vladimir Oltean
2020-10-19  3:49                   ` Florian Fainelli
2020-10-19 12:05                     ` Andrew Lunn
2020-10-19 16:27                       ` Florian Fainelli
2020-10-18 16:49   ` Jakub Kicinski
2020-10-18 17:36     ` Andrew Lunn
2020-10-18 18:26       ` Jakub Kicinski
2020-10-18 18:33         ` Jakub Kicinski
2020-10-17 21:36 ` [RFC PATCH 02/13] net: dsa: implement a central TX reallocation procedure Vladimir Oltean
2020-10-17 22:01   ` Vladimir Oltean
2020-10-17 22:11     ` Florian Fainelli
2020-10-17 22:17       ` Vladimir Oltean
2020-10-18  0:37         ` Florian Fainelli
2020-10-19  8:33       ` David Laight [this message]
2020-10-19 10:30         ` Vladimir Oltean
2020-10-19 11:14           ` David Laight
2020-10-19 11:41             ` Vladimir Oltean
2020-10-19 12:19           ` Andrew Lunn
2020-10-17 22:31     ` Vladimir Oltean
2020-10-18  0:13       ` Vladimir Oltean
2020-10-18 10:36         ` Christian Eggers
2020-10-18 11:42           ` Vladimir Oltean
2020-10-18 11:59             ` Christian Eggers
2020-10-18 12:15               ` Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 03/13] net: dsa: tag_ksz: don't allocate additional memory for padding/tagging Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 04/13] net: dsa: trailer: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 05/13] net: dsa: tag_qca: let DSA core deal with TX reallocation Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 06/13] net: dsa: tag_ocelot: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 07/13] net: dsa: tag_mtk: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 08/13] net: dsa: tag_lan9303: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 09/13] net: dsa: tag_edsa: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 10/13] net: dsa: tag_brcm: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 11/13] net: dsa: tag_dsa: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 12/13] net: dsa: tag_gswip: " Vladimir Oltean
2020-10-17 22:19   ` Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 13/13] net: dsa: tag_ar9331: " Vladimir Oltean
2020-10-17 23:07 ` [RFC PATCH 00/13] Generic TX reallocation for DSA Andrew Lunn

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