linux-kernel - Re: [PATCH net-next v2 1/2] net: mvneta: avoid getting status from rx

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Date:   Fri, 17 Feb 2017 14:35:21 +0100
From:   Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:     Jisheng Zhang <jszhang@...vell.com>
Cc:     <thomas.petazzoni@...e-electrons.com>, <davem@...emloft.net>,
        <arnd@...db.de>, <linux-arm-kernel@...ts.infradead.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2 1/2] net: mvneta: avoid getting status from rx_desc as much as possible

Hi Jisheng,
 
 On ven., févr. 17 2017, Jisheng Zhang <jszhang@...vell.com> wrote:

> In hot code path mvneta_rx_hwbm(), the rx_desc->status is read twice.
> The rx_desc is allocated by dma_alloc_coherent, it's uncacheable if
> the device isn't cache-coherent, reading from uncached memory is
> fairly slow. So reuse the read out rx_status to avoid the second
> reading from uncached memory.
>
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> Suggested-by: Arnd Bergmann <arnd@...db.de>

This one is OK and I didn't see a regression:

Tested-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>

Gregory


> ---
>  drivers/net/ethernet/marvell/mvneta.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index 61dd4462411c..06df72b8da85 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -313,8 +313,8 @@
>  	((addr >= txq->tso_hdrs_phys) && \
>  	 (addr < txq->tso_hdrs_phys + txq->size * TSO_HEADER_SIZE))
>  
> -#define MVNETA_RX_GET_BM_POOL_ID(rxd) \
> -	(((rxd)->status & MVNETA_RXD_BM_POOL_MASK) >> MVNETA_RXD_BM_POOL_SHIFT)
> +#define MVNETA_RX_GET_BM_POOL_ID(status) \
> +	(((status) & MVNETA_RXD_BM_POOL_MASK) >> MVNETA_RXD_BM_POOL_SHIFT)
>  
>  struct mvneta_statistic {
>  	unsigned short offset;
> @@ -1900,7 +1900,7 @@ static void mvneta_rxq_drop_pkts(struct mvneta_port *pp,
>  		for (i = 0; i < rx_done; i++) {
>  			struct mvneta_rx_desc *rx_desc =
>  						  mvneta_rxq_next_desc_get(rxq);
> -			u8 pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_desc);
> +			u8 pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_desc->status);
>  			struct mvneta_bm_pool *bm_pool;
>  
>  			bm_pool = &pp->bm_priv->bm_pools[pool_id];
> @@ -2075,7 +2075,7 @@ static int mvneta_rx_hwbm(struct mvneta_port *pp, int rx_todo,
>  		rx_bytes = rx_desc->data_size - (ETH_FCS_LEN + MVNETA_MH_SIZE);
>  		data = (u8 *)(uintptr_t)rx_desc->buf_cookie;
>  		phys_addr = rx_desc->buf_phys_addr;
> -		pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_desc);
> +		pool_id = MVNETA_RX_GET_BM_POOL_ID(rx_status);
>  		bm_pool = &pp->bm_priv->bm_pools[pool_id];
>  
>  		if (!mvneta_rxq_desc_is_first_last(rx_status) ||
> -- 
> 2.11.0
>

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com