Re: [net-next.git 3/7] stmmac: review private structure fields

[Eric Dumazet <eric.dumazet@gmail.com>]

On Wed, 2013-04-03 at 07:41 +0200, Giuseppe CAVALLARO wrote:
> recently many new supports have been added in the stmmac driver w/o taking care
> about where each new field had to be placed inside the private structure for
> guaranteeing the best cache usage.
> This is what I wanted in the beginning, so this patch reorganizes all the fields
> in order to keep adjacent fields for cache effect.
> I have also tried to optimize them by using pahole.
> 
> Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac.h |   70 +++++++++++++-------------
>  1 files changed, 35 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> index 75f997b..8aa28c5 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h
> @@ -35,36 +35,45 @@
>  
>  struct stmmac_priv {
>  	/* Frequently used values are kept adjacent for cache effect */
> -	struct dma_desc *dma_tx ____cacheline_aligned;	/* Basic TX desc */
> -	struct dma_extended_desc *dma_etx;	/* Extended TX descriptor */
> -	dma_addr_t dma_tx_phy;
> -	struct sk_buff **tx_skbuff;
> -	dma_addr_t *tx_skbuff_dma;
> +	struct dma_extended_desc *dma_etx;
> +	struct dma_desc *dma_tx ____cacheline_aligned_in_smp;
> +	struct sk_buff **tx_skbuff ____cacheline_aligned_in_smp;

dma_tx & tx_skbuff are readonly, why put them in separate cache lines ?

It seems there is an abuse of ____cacheline_aligned_in_smp in this
driver (especially if this driver only runs on UP arch)