Re: [dpdk-dev] [PATCH 1/2] net/mlx5: cache the associated network device ifindex

[Slava Ovsiienko <viacheslavo@mellanox.com>]

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Friday, July 19, 2019 21:03
> To: Slava Ovsiienko <viacheslavo@mellanox.com>
> Cc: dev@dpdk.org; Yongseok Koh <yskoh@mellanox.com>; Shahaf Shuler
> <shahafs@mellanox.com>
> Subject: Re: [PATCH 1/2] net/mlx5: cache the associated network device
> ifindex
> 
> On Fri, 19 Jul 2019 16:41:38 +0000
> Slava Ovsiienko <viacheslavo@mellanox.com> wrote:
> 
> > > -----Original Message-----
> > > From: Stephen Hemminger <stephen@networkplumber.org>
> > > Sent: Friday, July 19, 2019 19:16
> > > To: Slava Ovsiienko <viacheslavo@mellanox.com>
> > > Cc: dev@dpdk.org; Yongseok Koh <yskoh@mellanox.com>; Shahaf
> Shuler
> > > <shahafs@mellanox.com>
> > > Subject: Re: [PATCH 1/2] net/mlx5: cache the associated network
> > > device ifindex
> > >
> > > On Fri, 19 Jul 2019 05:31:44 +0000
> > > Viacheslav Ovsiienko <viacheslavo@mellanox.com> wrote:
> > >
> > > > +	/*
> > > > +	 * Store associated network device interface index. This index
> > > > +	 * is permanent throughout the lifetime of device. We do not spawn
> > > > +	 * rte_eth_dev ports without associated network device, and if
> > > > +	 * network device is being unbound we get the remove notification
> > > > +	 * message and rte_eth_dev port is also detached. So, we may store
> > > > +	 * the ifindex here and use the cached value further. The network
> > > > +	 * device name can be changed dynamically and should not be
> > > cached.
> > > > +	 */
> > > > +	assert(spawn->ifindex);
> > > > +	priv->if_index = spawn->ifindex;
> > >
> > > This correct, but overkill.
> > >
> > > 1. The comment is way too wordy. Please stick to only a couple of lines.
> > >    If you feel more explanation is necessary put that in the commit log.
> >
> > I'd prefer to see the issue description in the source,  not by
> > searching the git log for the appropriate commit. But OK, it does not
> matter.
> >
> > > 2. It is perfectly okay to return 0 as a value in dev_info.
> > >    Therefore the assert is unnecessary.
> >
> > Valid network interface index cannot be zero. For example,
> > if_nametoindex() returns zero in case of error. Also, in mlx5 we do
> > not spawn ports without attached network interfaces. Assert is not
> > related to dev_info, it checks whether the mlx5_dev_spawn() is called
> > with valid ifindex for valid port (ifindex checked against zero to validate
> infiniband port is active). We need this assert here.
> >
> > > 3. Where is "Reported-by:"
> > It is in cover letter:
> > "Proposed-by: Stephen Hemminger <stephen@networkplumber.org>"
> >  Sorry, I forgot to add this one in commit message, will fix.
> >
> > > 4. What was wrong with my simpler patch?
> > Please, see the cover letter. Your patch fixes only the part of
> > problem - the mlx5_dev_infos_get(). But it is just the case of unsafe
> mlx5_ifindex() usage.
> > mlx5_ifindex() itself must be fixed instead.
> >
> > WBR, Slava
> 
> Will your patch be backported to stable?
> It is critical that primary/secondary work on older releases.
Quite possible.
Is there the full-featured secondary processes support in 18.11 LTS?
I think it's worth to recheck the hotplug feature in 18.11 to avoid
ifindex unexpected change (try to unbound/rebound network device from/to PCI one,
check whether it is disabled/rejected, etc).

With best regards, Slava