netdev - RE: [PATCH bpf-next] xsk: update rings for load-acquire/store-release semantics

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Date:   Mon, 20 Jan 2020 17:24:52 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>,
        netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        bpf@...r.kernel.org, magnus.karlsson@...el.com,
        jonathan.lemon@...il.com
Subject: RE: [PATCH bpf-next] xsk: update rings for load-acquire/store-release
 semantics

Björn Töpel wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
> 
> Currently, the AF_XDP rings uses fences for the kernel-side
> produce/consume functions. By updating rings for
> load-acquire/store-release semantics, the full barrier (smp_mb()) on
> the consumer side can be replaced.
> 
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---
>  net/xdp/xsk_queue.h | 31 ++++++++++++++-----------------
>  1 file changed, 14 insertions(+), 17 deletions(-)
> 
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index bec2af11853a..2fff80576ee1 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -39,19 +39,18 @@ struct xsk_queue {
>  	u64 invalid_descs;
>  };

Should the xsk_cons_* libbpf routines also be updated then as well?
In general my understanding is the userspace and kernel should be
in sync?