From: Stephen Hemminger <stephen@networkplumber•org>
To: Tom Herbert <therbert@google•com>
Cc: David Miller <davem@davemloft•net>,
Linux Netdev List <netdev@vger•kernel.org>,
Eric Dumazet <edumazet@google•com>, Jerry Chu <hkchu@google•com>
Subject: Re: Get rxhash fixes and RFS support in tun
Date: Wed, 20 Nov 2013 17:12:32 -0800 [thread overview]
Message-ID: <20131120171232.518c29bb@nehalam.linuxnetplumber.net> (raw)
In-Reply-To: <CA+mtBx91hSmYKrbUsPrtnXRjYR8QDGZ+GAAnMixauUqw9LFkiQ@mail.gmail.com>
On Wed, 20 Nov 2013 17:09:01 -0800
Tom Herbert <therbert@google•com> wrote:
> On Wed, Nov 20, 2013 at 4:02 PM, David Miller <davem@davemloft•net> wrote:
> > From: Tom Herbert <therbert@google•com>
> > Date: Wed, 20 Nov 2013 12:25:48 -0800 (PST)
> >
> >> This patch series fixes some subtle bugs in tun use of skb->rxhash, all
> >> rxhash hash not be cleared appropraitely, and adds support for tun flows
> >> to work with RFS.
> >>
> >> Testing, in particular with tun, hasn't been completed yet.
> >
> > I think this needs to be reworked slightly.
> >
> > We really only have two boolean states:
> >
> > 1) Is the rxhash value in this SKB valid?
> >
> > 2) Is it a full L4 tuple hash?
> >
> > You are adding a "this is a SW computed hash" boolean state but I do
> > not think you should distinguish sw vs. hw especially. If the
> > hardware computed the rxhash on a tunneled packet in the
> > pre-decapsulated state, we very much want to recompute it, in
> > software, upon tunnel decapsulation in ip_tunnel_core.c
> >
> In either case it would be recomputed in SW if L4 hash was not set
> (i.e. no flow_dissector done finding L4). If L4 hash is set, that
> should refer to the hash of the inner 4-tuple, so I don't think you'd
> need to recompute it. I suppose there could be a case like encap in
> UDP where there are potentially two 4-tuples to deal with, but then
> the rxhash could just be cleared in decap to force recomputing hash
> over the inner packet-- even better I would hope that the trick of
> using outer source port to hold the hash of the inner packet (like in
> nvgre) is used so that the hash on the outer header is good for L4.
>
> The primary reason for sw_rhash is to know whether it is a comparable
> value to match against that of a flow whose hash was computed in SW
> (tun case).
You can't guarantee that two hardware hashes from different devices
are the same.
next prev parent reply other threads:[~2013-11-21 1:12 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-20 20:25 Get rxhash fixes and RFS support in tun Tom Herbert
2013-11-21 0:02 ` David Miller
2013-11-21 1:09 ` Tom Herbert
2013-11-21 1:12 ` Stephen Hemminger [this message]
2013-11-21 2:23 ` David Miller
2013-11-21 2:42 ` Tom Herbert
2013-11-21 2:50 ` David Miller
2013-11-21 16:28 ` Tom Herbert
2013-11-21 18:03 ` David Miller
2013-11-21 5:03 ` Jason Wang
2013-11-22 20:09 ` Tom Herbert
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=20131120171232.518c29bb@nehalam.linuxnetplumber.net \
--to=stephen@networkplumber$(echo .)org \
--cc=davem@davemloft$(echo .)net \
--cc=edumazet@google$(echo .)com \
--cc=hkchu@google$(echo .)com \
--cc=netdev@vger$(echo .)kernel.org \
--cc=therbert@google$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox