Re: [PATCH net-next 1/4] tun: rcu_deference xdp_prog only once per batch

[Jon Kohler <jon@nutanix.com>]

> On May 7, 2025, at 4:43 PM, Willem de Bruijn <willemdebruijn.kernel@gmail.com> wrote:
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> Jon Kohler wrote:
>> Hoist rcu_dereference(tun->xdp_prog) out of tun_xdp_one, so that
>> rcu_deference is called once during batch processing.
> 
> I'm skeptical that this does anything.
> 
> The compiler can inline tun_xdp_one and indeed seems to do so. And
> then it can cache the read in a register if that is the best use of
> a register.

The thought here is that if a compiler decided to not-inline tun_xdp_one
(perhaps it grew to big, or the compiler was being sassy), that the intent
would simply be that this wants to be called once-and-only-once. This
change just makes that intent more clear, and is a nice little cleanup.

I’ve got a series that stacks on top of this that enables multi-buffer support
and I can keep an eye on if that gets inlined or not.

> 
>> 
>> No functional change intended.
>> 
>> Signed-off-by: Jon Kohler <jon@nutanix.com>