netdev - Re: [PATCH RFC net-next 11/19] net: mvpp2: add flow control RXQ and BM pool config callbacks

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Date:   Sun, 10 Jan 2021 18:06:42 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     stefanc@...vell.com
Cc:     netdev@...r.kernel.org, thomas.petazzoni@...tlin.com,
        davem@...emloft.net, nadavh@...vell.com, ymarkman@...vell.com,
        linux-kernel@...r.kernel.org, kuba@...nel.org, mw@...ihalf.com,
        andrew@...n.ch, atenart@...nel.org
Subject: Re: [PATCH RFC net-next  11/19] net: mvpp2: add flow control RXQ and
 BM pool config callbacks

On Sun, Jan 10, 2021 at 05:30:15PM +0200, stefanc@...vell.com wrote:
> From: Stefan Chulski <stefanc@...vell.com>
> 
> This patch did not change any functionality.
> Added flow control RXQ and BM pool config callbacks that would be
> used to configure RXQ and BM pool thresholds.
> APIs also will disable/enable RXQ and pool Flow Control polling.
> 
> In this stage BM pool and RXQ has same stop/start thresholds
> defined in code.
> Also there are common thresholds for all RXQs.
> 
> Signed-off-by: Stefan Chulski <stefanc@...vell.com>
> ---
>  drivers/net/ethernet/marvell/mvpp2/mvpp2.h      |  51 +++++-
>  drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 169 ++++++++++++++++++++
>  2 files changed, 216 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
> index 4d58af6..0ba0598 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2.h
> @@ -763,10 +763,53 @@
>  		((kb) * 1024 - MVPP2_TX_FIFO_THRESHOLD_MIN)
>  
>  /* MSS Flow control */
> -#define MSS_SRAM_SIZE		0x800
> -#define FC_QUANTA		0xFFFF
> -#define FC_CLK_DIVIDER		0x140
> -#define MSS_THRESHOLD_STOP    768
> +#define MSS_SRAM_SIZE			0x800
> +#define MSS_FC_COM_REG			0
> +#define FLOW_CONTROL_ENABLE_BIT		BIT(0)
> +#define FLOW_CONTROL_UPDATE_COMMAND_BIT	BIT(31)
> +#define FC_QUANTA			0xFFFF
> +#define FC_CLK_DIVIDER			0x140
> +
> +#define MSS_BUF_POOL_BASE		0x40
> +#define MSS_BUF_POOL_OFFS		4
> +#define MSS_BUF_POOL_REG(id)		(MSS_BUF_POOL_BASE		\
> +					+ (id) * MSS_BUF_POOL_OFFS)
> +
> +#define MSS_BUF_POOL_STOP_MASK		0xFFF
> +#define MSS_BUF_POOL_START_MASK		(0xFFF << MSS_BUF_POOL_START_OFFS)
> +#define MSS_BUF_POOL_START_OFFS		12
> +#define MSS_BUF_POOL_PORTS_MASK		(0xF << MSS_BUF_POOL_PORTS_OFFS)
> +#define MSS_BUF_POOL_PORTS_OFFS		24
> +#define MSS_BUF_POOL_PORT_OFFS(id)	(0x1 <<				\
> +					((id) + MSS_BUF_POOL_PORTS_OFFS))
> +
> +#define MSS_RXQ_TRESH_BASE		0x200
> +#define MSS_RXQ_TRESH_OFFS		4
> +#define MSS_RXQ_TRESH_REG(q, fq)	(MSS_RXQ_TRESH_BASE + (((q) + (fq)) \
> +					* MSS_RXQ_TRESH_OFFS))
> +
> +#define MSS_RXQ_TRESH_START_MASK	0xFFFF
> +#define MSS_RXQ_TRESH_STOP_MASK		(0xFFFF << MSS_RXQ_TRESH_STOP_OFFS)
> +#define MSS_RXQ_TRESH_STOP_OFFS		16
> +
> +#define MSS_RXQ_ASS_BASE	0x80
> +#define MSS_RXQ_ASS_OFFS	4
> +#define MSS_RXQ_ASS_PER_REG	4
> +#define MSS_RXQ_ASS_PER_OFFS	8
> +#define MSS_RXQ_ASS_PORTID_OFFS	0
> +#define MSS_RXQ_ASS_PORTID_MASK	0x3
> +#define MSS_RXQ_ASS_HOSTID_OFFS	2
> +#define MSS_RXQ_ASS_HOSTID_MASK	0x3F
> +
> +#define MSS_RXQ_ASS_Q_BASE(q, fq) ((((q) + (fq)) % MSS_RXQ_ASS_PER_REG)	 \
> +				  * MSS_RXQ_ASS_PER_OFFS)
> +#define MSS_RXQ_ASS_PQ_BASE(q, fq) ((((q) + (fq)) / MSS_RXQ_ASS_PER_REG) \
> +				   * MSS_RXQ_ASS_OFFS)
> +#define MSS_RXQ_ASS_REG(q, fq) (MSS_RXQ_ASS_BASE + MSS_RXQ_ASS_PQ_BASE(q, fq))
> +
> +#define MSS_THRESHOLD_STOP	768
> +#define MSS_THRESHOLD_START	1024
> +
>  
>  /* RX buffer constants */
>  #define MVPP2_SKB_SHINFO_SIZE \
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> index bc4b8069..19648c4 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> @@ -744,6 +744,175 @@ static void *mvpp2_buf_alloc(struct mvpp2_port *port,
>  	return data;
>  }
>  
> +/* Routine calculate single queue shares address space */
> +static int mvpp22_calc_shared_addr_space(struct mvpp2_port *port)
> +{
> +	/* If number of CPU's greater than number of threads, return last
> +	 * address space
> +	 */
> +	if (num_active_cpus() >= MVPP2_MAX_THREADS)
> +		return MVPP2_MAX_THREADS - 1;
> +
> +	return num_active_cpus();

Firstly - this can be written as:

	return min(num_active_cpus(), MVPP2_MAX_THREADS - 1);

Secondly - what if the number of active CPUs change, for example due
to hotplug activity. What if we boot with maxcpus=1 and then bring the
other CPUs online after networking has been started? The number of
active CPUs is dynamically managed via the scheduler as CPUs are
brought online or offline.

> +/* Routine enable flow control for RXQs conditon */
> +void mvpp2_rxq_enable_fc(struct mvpp2_port *port)
...
> +/* Routine disable flow control for RXQs conditon */
> +void mvpp2_rxq_disable_fc(struct mvpp2_port *port)

Nothing seems to call these in this patch, so on its own, it's not
obvious how these are being called, and therefore what remedy to
suggest for num_active_cpus().

-- 
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