On 2024-05-06 16:09:47 [-0700], Alexei Starovoitov wrote:

quoted

quoted

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?

[...]

quoted

+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...

quoted

+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