netdev.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Vladimir Oltean <olteanv@gmail.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Christian Eggers <ceggers@arri.de>,
	Kurt Kanzenbach <kurt@linutronix.de>,
	Woojung Huh <woojung.huh@microchip.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>,
	"David S . Miller" <davem@davemloft.net>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: dsa: ksz: fix padding size of skb
Date: Fri, 16 Oct 2020 21:13:19 +0300	[thread overview]
Message-ID: <20201016181319.2jrbdp5h7avzjczj@skbuf> (raw)
In-Reply-To: <20201016110311.6a43e10d@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>

On Fri, Oct 16, 2020 at 11:03:11AM -0700, Jakub Kicinski wrote:
> On Fri, 16 Oct 2020 18:56:45 +0300 Vladimir Oltean wrote:
> > > 3. "Manually" unsharing in dsa_slave_xmit(), reserving enough tailroom
> > > for the tail tag (and ETH_ZLEN?). Would moving the "else" clause from
> > > ksz_common_xmit()  to dsa_slave_xmit() do the job correctly?  
> > 
> > I was thinking about something like that, indeed. DSA knows everything
> > about the tagger: its overhead, whether it's a tail tag or not. The xmit
> > callback of the tagger should only be there to populate the tag where it
> > needs to be. But reallocation, padding, etc etc, should all be dealt
> > with by the common DSA xmit procedure. We want the taggers to be simple
> > and reuse as much logic as possible, not to be bloated.
> 
> FWIW if you want to avoid the reallocs you may want to set
> needed_tailroom on the netdev.

Tell me more about that, I've been meaning since forever to try it out.
I read about needed_headroom and needed_tailroom, and it's one of the
reasons why I added the .tail_tag option in the DSA tagger (to
distinguish whether a switch needs headroom or tailroom), but I can't
figure out, just from static analysis of the code, where exactly is the
needed tailroom being accounted for. For example, if I'm in Christian's
situation, e.g. I have a packet smaller than ETH_ZLEN, would the
tailroom be enough to hold just the dev->needed_tailroom, or would there
be enough space in the skb for the entire ETH_ZLEN + dev->needed_tailroom?

  reply	other threads:[~2020-10-16 18:13 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-14 16:17 Christian Eggers
2020-10-14 16:47 ` Vladimir Oltean
2020-10-14 16:54   ` Vladimir Oltean
2020-10-14 17:02     ` Christian Eggers
2020-10-14 17:31       ` Vladimir Oltean
2020-10-15 17:58         ` Christian Eggers
2020-10-16  7:45           ` Kurt Kanzenbach
2020-10-16  9:00             ` Christian Eggers
2020-10-16  9:05               ` Vladimir Oltean
2020-10-16 12:44                 ` Christian Eggers
2020-10-16 15:56                   ` Vladimir Oltean
2020-10-16 18:03                     ` Jakub Kicinski
2020-10-16 18:13                       ` Vladimir Oltean [this message]
2020-10-16 18:52                         ` Jakub Kicinski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20201016181319.2jrbdp5h7avzjczj@skbuf \
    --to=olteanv@gmail.com \
    --cc=UNGLinuxDriver@microchip.com \
    --cc=andrew@lunn.ch \
    --cc=ceggers@arri.de \
    --cc=davem@davemloft.net \
    --cc=f.fainelli@gmail.com \
    --cc=kuba@kernel.org \
    --cc=kurt@linutronix.de \
    --cc=linux-kernel@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=vivien.didelot@gmail.com \
    --cc=woojung.huh@microchip.com \
    --subject='Re: [PATCH net] net: dsa: ksz: fix padding size of skb' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).