netdev - Re: [PATCH v2 net-next 10/11] qede: Add basic XDP support

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Date:   Tue, 29 Nov 2016 17:51:31 +0000
From:   "Mintz, Yuval" <Yuval.Mintz@...ium.com>
To:     Jakub Kicinski <kubakici@...pl>,
        Daniel Borkmann <daniel@...earbox.net>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>
Subject: Re: [PATCH v2 net-next 10/11] qede: Add basic XDP support

> > You also need to wrap this under rcu_read_lock() (at least I haven't seen
> > it in your patches) for same reasons as stated in 326fe02d1ed6 ("net/mlx4_en:
> > protect ring->xdp_prog with rcu_read_lock"), as otherwise xdp_prog could
> > disappear underneath you. mlx4 and nfp does it correctly, looks like mlx5
> > doesn't.

> My understanding was that Yuval is always doing full stop()/start() so
> there should be no RX packets in flight while the XDP prog is being
> changed.  But thinking about it again, perhaps is worth adding the
> optimization to forego the full qede_reload() in qede_xdp_set() if there
> is a program already loaded and just do the xchg()+put() (and add RCU
> protection on the fast path)?

Yeps. That the current state of the code.
I'll surely pursue this later, but I don't think all this added complexity
is required for the initial submission.

BTW, one of the problems [or perhaps 'lack of motivation' is a better term]
I had with the program switching scenario was that there was no sample
application that did it.
If it's really an interesting [basic] scenario, perhaps it's worthy to add
a sample user app. that will repeatedly switch the attached eBPF?