netdev - Re: [PATCH net] net: mvneta: fix operation for 64K PAGE

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Date:   Wed, 12 Dec 2018 02:48:22 +0000
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Marcin Wojtas <mw@...ihalf.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "antoine.tenart@...tlin.com" <antoine.tenart@...tlin.com>,
        "jaz@...ihalf.com" <jaz@...ihalf.com>,
        "gregory.clement@...tlin.com" <gregory.clement@...tlin.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "maxime.chevallier@...tlin.com" <maxime.chevallier@...tlin.com>,
        "nadavh@...vell.com" <nadavh@...vell.com>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        "stefanc@...vell.com" <stefanc@...vell.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH net] net: mvneta: fix operation for 64K PAGE_SIZE

Hi,

On Tue, 11 Dec 2018 13:56:49 +0100 Marcin Wojtas wrote:

> Recent changes in the mvneta driver reworked allocation
> and handling of the ingress buffers to use entire pages.
> Apart from that in SW BM scenario the HW must be informed
> via PRXDQS about the biggest possible incoming buffer
> that can be propagated by RX descriptors.
> 
> The BufferSize field was filled according to the MTU-dependent
> pkt_size value. Later change to PAGE_SIZE broke RX operation
> when usin 64K pages, as the field is simply too small.
> 
> This patch conditionally limits the value passed to the BufferSize
> of the PRXDQS register, depending on the PAGE_SIZE used.
> On the occasion remove now unused frag_size field of the mvneta_port
> structure.
> 
> Fixes: 562e2f467e71 ("net: mvneta: Improve the buffer allocation
> method for SWBM")

IMHO, we'd better revert 562e2f467e71 and 7e47fd84b56bb

The issue commit 562e2f467e71 wants to solve is due to commit 7e47fd84b56bb
It looks a bit wired, to introduce regression then submit another commit(in
the same patch set) solve it

Per my test, after reverting 562e2f467e71 and 7e47fd84b56bb, I can't reproduce
what's claimed in commit 562e2f467e71 -- "With system having a small memory
(around 256MB), the state "cannot allocate memory to refill with new buffer"
is reach pretty quickly."


> 
> Signed-off-by: Marcin Wojtas <mw@...ihalf.com>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index e5397c8..61b2349 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -408,7 +408,6 @@ struct mvneta_port {
>  	struct mvneta_pcpu_stats __percpu	*stats;
>  
>  	int pkt_size;
> -	unsigned int frag_size;
>  	void __iomem *base;
>  	struct mvneta_rx_queue *rxqs;
>  	struct mvneta_tx_queue *txqs;
> @@ -2905,7 +2904,9 @@ static void mvneta_rxq_hw_init(struct mvneta_port *pp,
>  	if (!pp->bm_priv) {
>  		/* Set Offset */
>  		mvneta_rxq_offset_set(pp, rxq, 0);
> -		mvneta_rxq_buf_size_set(pp, rxq, pp->frag_size);
> +		mvneta_rxq_buf_size_set(pp, rxq, PAGE_SIZE < SZ_64K ?
> +					PAGE_SIZE :
> +					MVNETA_RX_BUF_SIZE(pp->pkt_size));
>  		mvneta_rxq_bm_disable(pp, rxq);
>  		mvneta_rxq_fill(pp, rxq, rxq->size);
>  	} else {
> @@ -3760,7 +3761,6 @@ static int mvneta_open(struct net_device *dev)
>  	int ret;
>  
>  	pp->pkt_size = MVNETA_RX_PKT_SIZE(pp->dev->mtu);
> -	pp->frag_size = PAGE_SIZE;
>  
>  	ret = mvneta_setup_rxqs(pp);
>  	if (ret)