Re: [PATCH bpf 1/2] bpf: Load ringbuf consumer_pos under the spinlock

[Alexei Starovoitov]

On Fri, Oct 16, 2026 at 12:33 AM Igor Malovitsa <igor.malovitsa@xxxxxxxxx> wrote:
> -	cons_pos = smp_load_acquire(&rb->consumer_pos);
> -
>  	if (raw_res_spin_lock_irqsave(&rb->spinlock, flags))
>  		return NULL;
>
> +	/* Under the lock, so at most one ring behind producer_pos. */
> +	cons_pos = smp_load_acquire(&rb->consumer_pos);
> +

libbpf writes consumer_pos after every record, so this load is
a cache miss most of the time.
Today it's done before the lock. With this patch all other producers
spin on the lock while this cpu waits for it. On 64-bit too.
So "Neither changes anything on 64-bit" in the cover letter is not correct.

imo it's not worth slowing down everyone for that.

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