Re: [PATCH net-next 14/15] net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.

[Sebastian Andrzej Siewior]

On 2024-05-06 16:09:47 [-0700], Alexei Starovoitov wrote:
> > > On PREEMPT_RT the pointer to bpf_net_context is saved task's
> > > task_struct. On non-PREEMPT_RT builds the pointer saved in a per-CPU
> > > variable (which is always NODE-local memory). Using always the
> > > bpf_net_context approach has the advantage that there is almost zero
> > > differences between PREEMPT_RT and non-PREEMPT_RT builds.
> >
> > Did you ever manage to get any performance data to see if this has an
> > impact?
> >
> > [...]
> >
> > > +static inline struct bpf_net_context *bpf_net_ctx_get(void)
> > > +{
> > > +     struct bpf_net_context *bpf_net_ctx = this_cpu_read(bpf_net_context);
> > > +
> > > +     WARN_ON_ONCE(!bpf_net_ctx);
> >
> > If we have this WARN...
> >
> > > +static inline struct bpf_redirect_info *bpf_net_ctx_get_ri(void)
> > > +{
> > > +     struct bpf_net_context *bpf_net_ctx = bpf_net_ctx_get();
> > > +
> > > +     if (!bpf_net_ctx)
> > > +             return NULL;
> >
> > ... do we really need all the NULL checks?
> 
> Indeed.
> Let's drop all NULL checks, since they definitely add overhead.
> I'd also remove ifdef CONFIG_PREEMPT_RT and converge on single implementation:
> static inline struct bpf_net_context * bpf_net_ctx_get(void)
> {
>  return current->bpf_net_context;
> }

Okay, let me do that then.

Sebastian