netdev - RE: [Intel-wired-lan] [PATCH bpf-next 4/6] xsk: introduce padding between more ring pointers

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Date:   Mon, 09 Nov 2020 12:43:43 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Magnus Karlsson <magnus.karlsson@...il.com>,
        magnus.karlsson@...el.com, bjorn.topel@...el.com, ast@...nel.org,
        daniel@...earbox.net, netdev@...r.kernel.org,
        jonathan.lemon@...il.com
Cc:     maciejromanfijalkowski@...il.com, intel-wired-lan@...ts.osuosl.org,
        bpf@...r.kernel.org
Subject: RE: [Intel-wired-lan] [PATCH bpf-next 4/6] xsk: introduce padding
 between more ring pointers

Magnus Karlsson wrote:
> From: Magnus Karlsson <magnus.karlsson@...el.com>
> 
> Introduce one cache line worth of padding between the consumer pointer
> and the flags field as well as between the flags field and the start
> of the descriptors in all the lockless rings. This so that the x86 HW
> adjacency prefetcher will not prefetch the adjacent pointer/field when
> only one pointer/field is going to be used. This improves throughput
> performance for the l2fwd sample app with 1% on my machine with HW
> prefetching turned on in the BIOS.
> 
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---

Acked-by: John Fastabend <john.fastabend@...il.com>

>  net/xdp/xsk_queue.h | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index cdb9cf3..74fac80 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -18,9 +18,11 @@ struct xdp_ring {
>  	/* Hinder the adjacent cache prefetcher to prefetch the consumer
>  	 * pointer if the producer pointer is touched and vice versa.
>  	 */
> -	u32 pad ____cacheline_aligned_in_smp;
> +	u32 pad1 ____cacheline_aligned_in_smp;
>  	u32 consumer ____cacheline_aligned_in_smp;
> +	u32 pad2 ____cacheline_aligned_in_smp;
>  	u32 flags;
> +	u32 pad3 ____cacheline_aligned_in_smp;
>  };
>  
>  /* Used for the RX and TX queues for packets */
> -- 
> 2.7.4
> 
> _______________________________________________
> Intel-wired-lan mailing list
> Intel-wired-lan@...osl.org
> https://lists.osuosl.org/mailman/listinfo/intel-wired-lan

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