Message-ID: <20110114183816.GB1288@mcarlson.broadcom.com>
Date:	Fri, 14 Jan 2011 10:38:16 -0800
From:	"Matt Carlson" <mcarlson@...adcom.com>
To:	"Jesse Gross" <jesse@...ira.com>
cc:	"Matthew Carlson" <mcarlson@...adcom.com>,
	"Michael Leun" <lkml20101129@...ton.leun.net>,
	"Michael Chan" <mchan@...adcom.com>,
	"Eric Dumazet" <eric.dumazet@...il.com>,
	"David Miller" <davem@...emloft.net>,
	"Ben Greear" <greearb@...delatech.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 2.6.36] vlan: Avoid hwaccel vlan packets when vid
 not used

On Fri, Jan 14, 2011 at 09:49:47AM -0800, Jesse Gross wrote:
> On Thu, Jan 13, 2011 at 8:15 PM, Matt Carlson <mcarlson@...adcom.com> wrote:
> > On Thu, Jan 13, 2011 at 01:58:40PM -0800, Jesse Gross wrote:
> >> On Thu, Jan 13, 2011 at 3:50 PM, Matt Carlson <mcarlson@...adcom.com> wrote:
> >> > On Thu, Jan 13, 2011 at 07:06:22AM -0800, Jesse Gross wrote:
> >> >> On Wed, Jan 12, 2011 at 8:21 PM, Matt Carlson <mcarlson@...adcom.com> wrote:
> >> >> > On Thu, Jan 06, 2011 at 08:36:27PM -0800, Jesse Gross wrote:
> >> >> >> On Thu, Jan 6, 2011 at 10:24 PM, Matt Carlson <mcarlson@...adcom.com> wrote:
> >> >> >> > On Sat, Dec 18, 2010 at 07:38:00PM -0800, Jesse Gross wrote:
> >> >> >> >> On Tue, Dec 14, 2010 at 11:16 PM, Michael Leun
> >> >> >> >> <lkml20101129@...ton.leun.net> wrote:
> >> >> >> >> > OK - all tests done on that DL320G5:
> >> >> >> >> >
> >> >> >> >> > For completeness, 2.6.37-rc5 unpatched:
> >> >> >> >> >
> >> >> >> >> > eth0, no vlan configured: totally broken - see double tagged vlans
> >> >> >> >> > without tag, single or untagged packets missing at all
> >> >> >> >>
> >> >> >> >> Random behavior? ?This one is somewhat hard to explain - maybe there
> >> >> >> >> are some other factors. ?eth0 has ASF on, so it always strips tags. ?I
> >> >> >> >> would expect it to behave like the vlan configured case.
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> > eth0, vlan configured: see packets without vlan tag (see double tagged
> >> >> >> >> > packets with one vlan tag)
> >> >> >> >>
> >> >> >> >> Both ASF and vlan group configured cause tag stripping to be enabled.
> >> >> >> >> Missing tag.
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> > eth1 same as originally reported:
> >> >> >> >> > without vlan configured see vlan tags (single and double tagged as
> >> >> >> >> > expected)
> >> >> >> >>
> >> >> >> >> No ASF and no vlan group means tag stripping is disabled. ?Have tag.
> >> >> >> >>
> >> >> >> >> > with vlan configured: see packets without vlan tag (see double tagged
> >> >> >> >> > packets with one vlan tag)
> >> >> >> >>
> >> >> >> >> Configuring vlan group causes stripping to be enabled. ?Missing tag.
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> >
> >> >> >> >> > 2.6.37-rc5, your tg3 use new vlan-code patch:
> >> >> >> >> >
> >> >> >> >> > eth0, no vlan configured: ?see packets without vlan tag (see double
> >> >> >> >> > tagged packets with one vlan tag)
> >> >> >> >>
> >> >> >> >> ASF enables tag stripping. ?Missing tag.
> >> >> >> >>
> >> >> >> >> > eth1, no vlan configured: see vlan tags (single and double tagged as
> >> >> >> >> > expected)
> >> >> >> >>
> >> >> >> >> No ASF, no vlan group means no stripping. ?Have tag.
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> >
> >> >> >> >> > eth0, vlan configured: as without vlan
> >> >> >> >>
> >> >> >> >> ASF enables stripping. ?Missing tag.
> >> >> >> >>
> >> >> >> >> > eth1, vlan configured: as without vlan
> >> >> >> >>
> >> >> >> >> With this patch vlan stripping is only enabled when ASF is on, so no
> >> >> >> >> stripping. ?Have tag.
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> > 2.6.37-rc5, your tg3 use new vlan-code patch with test patch ontop
> >> >> >> >> >
> >> >> >> >> > eth1 no vlan configured: see packets without vlan tag (see double tagged
> >> >> >> >> > packets with one vlan tag)
> >> >> >> >>
> >> >> >> >> With the second patch, vlan stripping is always enabled. ?Missing tag.
> >> >> >> >>
> >> >> >> >> > eth1 with vlan: the same
> >> >> >> >>
> >> >> >> >> Stripping still always enabled. ?Missing tag.
> >> >> >> >>
> >> >> >> >> The bottom line is whenever vlan stripping is enabled we're missing
> >> >> >> >> the outer tag. ?It might be worth adding some debugging in the area
> >> >> >> >> before napi_gro_receive/vlan_gro_receive (depending on version). ?My
> >> >> >> >> guess is that (desc->type_flags & RXD_FLAG_VLAN) is false even for
> >> >> >> >> vlan packets on this NIC.
> >> >> >> >>
> >> >> >> >> You said that everything works on the 5752? ?Matt, is it possible that
> >> >> >> >> the 5714 either has a problem with vlan stripping or a different way
> >> >> >> >> of reporting it?
> >> >> >> >
> >> >> >> > I don't think this is a 5714 specific issue. ?I think the problem is
> >> >> >> > rooted in the fact that the VLAN tag stripping is enabled.
> >> >> >>
> >> >> >> It's definitely related to vlan stripping being enabled. ?Other cards
> >> >> >> using tg3 seem to work fine with stripping though, which is why I
> >> >> >> thought it might be specific to the 5714.
> >> >> >
> >> >> > I just tested this on a 5714S, using a net-next-2.6 snapshot obtained
> >> >> > today. ?It does the right thing in both cases (2nd tg3 patch ommited /
> >> >> > applied). ?The tag is always visible in the packet stream as seen from
> >> >> > tcpdump.
> >> >> >
> >> >> >> > Your RXD_FLAG_VLAN idea sounds unlikely to me, but it's worth a check.
> >> >> >> >
> >> >> >> > The patch here is using __vlan_hwaccel_put_tag(), which informs the
> >> >> >> > stack a VLAN tag is present. ?If this is indeed a reporting problem, I'm
> >> >> >> > not sure what else the driver should be doing.
> >> >> >>
> >> >> >> The code to hand off the tag to the stack looks OK to me. ?Michael was
> >> >> >> seeing this on older versions of the kernel as well with this NIC,
> >> >> >> which predates both this patch and the larger vlan changes so it
> >> >> >> doesn't seem like a problem with passing the tag to the network stack.
> >> >> >> ?It's hard to know exactly what is going on though without seeing what
> >> >> >> the hardware is reporting.
> >> >> >
> >> >> > When RX_MODE_KEEP_VLAN_TAG is set, the RXD_FLAG_VLAN flag will not be set
> >> >> > when receiving a packet. ?The driver skips the __vlan_hwaccel_put_tag()
> >> >> > call.
> >> >> >
> >> >> > When RX_MODE_KEEP_VLAN_TAG is unset, the RXD_FLAG_VLAN flag is set, and
> >> >> > __vlan_hwaccel_put_tag() is called to reinject the packet.
> >> >>
> >> >> OK, thanks for testing it out. ?I'm not sure that there's anything
> >> >> more we can do without hearing from Michael.
> >> >
> >> > In the meantime, I think what we have should go upstream. ?Just to be
> >> > absolutely clear though, your position is that VLAN tags should always
> >> > be stripped?
> >>
> >> That's what the other converted drivers do by default (though most of
> >> them also provide an ethtool set_flags() method to change this). ?It's
> >> generally the most efficient and is now safe to do in all cases. ?It's
> >> also the consistent with what was happening before, since stripping
> >> was enabled when a vlan device was configured. ?So, yes, normally I
> >> think stripping should be enabled.
> >>
> >> I assumed that disabling stripping in most situations was just an
> >> oversight. ?Was there a reason why you feel it is better not to use
> >> it?
> >
> > Actually, the tg3 driver was trying to disable VLAN tag stripping
> > when possible. ?I believe this was primarily to support the raw packet
> > interface.
> 
> Hmm, is this really true?
> 
>         if (!tp->vlgrp &&
>             !(tp->tg3_flags & TG3_FLAG_ENABLE_ASF))
>                 rx_mode |= RX_MODE_KEEP_VLAN_TAG;
> 
> So if a vlan device is registered or ASF is enabled we will use
> stripping.  That seems like it is using stripping in the common case
> when vlans are used.

Right.

> Before 2.6.37 it was only possible to deliver stripped tags if a vlan
> group was configured.  This means that if ASF was enabled and forced
> stripping but no group was configured we would lose the tag.  In this
> situation tg3 manually reinserts the tags so raw packet capture will
> see them, as you say.

Right.  VLAN tagged frames can still arrive if CONFIG_VLAN_8021Q or
CONFIG_VLAN_8021Q_MODULE is not set.  That's why the driver was trying
to keep them inline.  To eliminate the unnecessary overhead of
reinjecting the VLAN tag.

> However, in the current tree this limitation no
> longer exists and it is always possible to deliver stripped tags to
> the networking core, which should do the right thing in all
> situations.

Yes.  Even though the stack is capable of reinjecting the VLAN tag,
doesn't it make sense to avoid that if we knew they would never be
needed out-of-packet?

> So I believe the only reason to disable tag stripping is for debugging
> or some other special purpose situation.

Nope.  I think we covered it all.  Thanks for the info.

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