netdev - Re: [bpf-next V2 PATCH 01/14] xdp: base API for new XDP rx-queue info concept

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Date:   Fri, 22 Dec 2017 16:14:43 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        netdev@...r.kernel.org, dsahern@...il.com, gospo@...adcom.com,
        bjorn.topel@...el.com, michael.chan@...adcom.com
Subject: Re: [bpf-next V2 PATCH 01/14] xdp: base API for new XDP rx-queue
 info concept

On Fri, 22 Dec 2017 18:11:39 +0100, Jesper Dangaard Brouer wrote:
> +struct xdp_rxq_info {
> +	struct net_device *dev;
> +	u32 queue_index;
> +	u32 reg_state;
> +} ____cacheline_aligned; /* perf critical, avoid false-sharing */

I'm assuming this is cacheline_aligned, because of some stuff you will
add here in the future for the completion path?  (The comment could
mention that this data is read-mostly.)  Drivers are likely to already
have a read-mostly (or unused-mostly) section of the rx ring structure.
Would it be possible to define this in a way that would allow people
who carefully lay out their data path structures to save cache space?