From: Adrien Mazarguil <adrien.mazarguil@6wind.com>
To: Thomas Monjalon <thomas@monjalon.net>
Cc: dev@dpdk.org, Gaetan Rivet <gaetan.rivet@6wind.com>,
Ferruh Yigit <ferruh.yigit@intel.com>,
David Marchand <david.marchand@redhat.com>,
stable@dpdk.org, Ali Alnubani <alialnu@mellanox.com>
Subject: Re: [dpdk-stable] [dpdk-dev] [PATCH v2] net/failsafe: fix source port ID in Rx packets
Date: Thu, 18 Apr 2019 19:09:03 +0200 [thread overview]
Message-ID: <20190418170903.GI4889@6wind.com> (raw)
In-Reply-To: <1609324.Zy8sxAcIVK@xps>
On Thu, Apr 18, 2019 at 06:54:22PM +0200, Thomas Monjalon wrote:
<snip>
> > <snip>
> > > > "slave" is a wording from bonding.
> > > > In failsafe, it is sub-device, isn't it?
> >
> > I don't mind, although grep shows a couple of comments talking about slaves
> > already. Either way I think it fits as those are failsafe's pets, as in
> > failsafe does whatever it wants to them and they don't have a say :)
> >
> > Does it warrant a v3?
>
> Yes please, except if Ferruh is already doing the change on apply.
Will do.
<snip>
> > > > I'm afraid the performance drop to be hard.
> >
> > Mbufs are still hot from the oven at this stage, so it's not *that*
> > expensive. I don't see a more efficient approach.
>
> Yes, Ali did some quick tests showing no perf drop.
Great.
> > > > How the port id in mbuf is used exactly?
> >
> > Applications that dissociate Rx itself from packet processing, or whenever a
> > networking stack is involved. Basically every time some code wonders where a
> > packet comes from due to lack of context and looks at m->port for the
> > answer (e.g. checking that a packet arrives on the right port given its
> > destination address).
> >
> > > > What crash are you seeing?
> >
> > None, thankfully. In my specific use case, 6WINDGate's stack simply drops
> > traffic coming from unknown ports.
> >
> > However nothing prevents applications from using m->port as an index of some
> > array they allocated to quickly retrieve port context without looking it
> > up. They wouldn't expect indices they do not know about in there; assuming
> > it will result in a crash is not far fetched.
> >
> > > Another way to fix it without performance drop would be to add
> > > a new driver op to set the top-level port id.
> > > This top-level id would be stored in the private structure of the port,
> > > initialized with the port id of the port itself, and used to fill mbufs.
> > >
> > > Thoughts?
> >
> > Adding a new devop as a fix would be a problem for stable releases, so this
> > patch is definitely needed, at least as a first step.
> >
> > I'm not against a new API, however would it be worth the trouble? Especially
> > considering it would only be used by failsafe-like drivers with something to
> > hide from applications which is not the main use case.
> >
> > For some PMDs, this operation could only be done at init time before port ID
> > is stored in private Rx queue data for fast retrieval. Retrieving it through
> > a pointer so it can be updated anytime would make it more expensive than
> > necessary for them.
>
> I don't understand this comment.
> The port id is currently retrieved via some pointers already.
> I suggest to look at private structure, it is not different.
See "rep->port = rxq->port_id" in mlx4_rxtx.c for instance. Port ID is
cached in private queue data structure (struct rxq) and retrieved there to
avoid looking it up in non-local data structure rxq->priv->dev_data->port.
In fact rxq->priv is not accessed even once during Rx.
> > It's understood that having failsafe in the dataplane has a cost, but even
> > with the proposed fix, that cost is dwarfed by the amount of work done by a
> > true PMD (and the application) for Rx processing.
> >
> > My suggestion is to wait for someone to complain about the performance
> > compared to what they had before that fix, only then see what we can do.
>
> OK
>
>
--
Adrien Mazarguil
6WIND
next prev parent reply other threads:[~2019-04-18 17:09 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190418130419.25675-1-adrien.mazarguil@6wind.com>
2019-04-18 15:32 ` [dpdk-stable] " Adrien Mazarguil
2019-04-18 15:39 ` [dpdk-stable] [dpdk-dev] " Thomas Monjalon
2019-04-18 15:51 ` Thomas Monjalon
2019-04-18 16:46 ` Adrien Mazarguil
2019-04-18 16:54 ` Thomas Monjalon
2019-04-18 17:09 ` Adrien Mazarguil [this message]
2019-04-18 17:43 ` Thomas Monjalon
2019-04-18 15:51 ` Gaëtan Rivet
2019-04-18 17:20 ` [dpdk-stable] [PATCH v3] " Adrien Mazarguil
2019-04-18 18:51 ` Ferruh Yigit
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