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From: Vladimir Oltean <vladimir.oltean@nxp.com>
To: Christian Eggers <ceggers@arri.de>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"andrew@lunn.ch" <andrew@lunn.ch>,
	"f.fainelli@gmail.com" <f.fainelli@gmail.com>,
	"vivien.didelot@gmail.com" <vivien.didelot@gmail.com>,
	"kuba@kernel.org" <kuba@kernel.org>,
	Kurt Kanzenbach <kurt@linutronix.de>
Subject: Re: [RFC PATCH 02/13] net: dsa: implement a central TX reallocation procedure
Date: Sun, 18 Oct 2020 12:15:39 +0000
Message-ID: <20201018121538.usz7zzb5c7zsar42@skbuf> (raw)
In-Reply-To: <9012784.ALUgdZc4HQ@n95hx1g2>

On Sun, Oct 18, 2020 at 01:59:43PM +0200, Christian Eggers wrote:
> On Sunday, 18 October 2020, 13:42:06 CEST, Vladimir Oltean wrote:
> > On Sun, Oct 18, 2020 at 12:36:03PM +0200, Christian Eggers wrote:
> > > >       err = pskb_expand_head(skb, max(needed_headroom, 0),
> > > >
> > > >                              max(needed_tailroom, 0), GFP_ATOMIC);
> > >
> > > You may remove the second max() statement (around needed_tailroom). This
> > > would size the reallocated skb more exactly to the size actually required
> > > an may save some RAM (already tested too).
> >
> > Please explain more. needed_tailroom can be negative, why should I
> > shrink the tailroom?
> Because it will not be required anymore. This may lead to smaller memory
> allocations or the excess tailroom can be reused for headroom if needed. If
> none of both applies, the tailroom will not be changed.

Understand now, you're talking about the case where the tailroom in the
skb is already larger than what we estimate the packet will need through
its entire journey in the TX path. I still won't shrink it though, I'll
keep using the second approach you suggested.

  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
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 [this message]
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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