linux-kernel - Re: [PATCH net-next 2/3] net: mvpp2: adjust gso stop wake thresholds

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Message-Id: <20180227.111306.790069240486489244.davem@davemloft.net>
Date:   Tue, 27 Feb 2018 11:13:06 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     antoine.tenart@...tlin.com
Cc:     ymarkman@...vell.com, mw@...ihalf.com, stefanc@...vell.com,
        thomas.petazzoni@...e-electrons.com,
        gregory.clement@...e-electrons.com,
        miquel.raynal@...e-electrons.com, nadavh@...vell.com,
        maxime.chevallier@...tlin.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] net: mvpp2: adjust gso stop wake
 thresholds

From: Antoine Tenart <antoine.tenart@...tlin.com>
Date: Mon, 26 Feb 2018 15:14:26 +0100

> From: Yan Markman <ymarkman@...vell.com>
> 
> Adjust MVPP2_MAX_TSO_SEGS and stop_threshold/wake_threshold
> for better TXQ utilization and performance.
> 
> Signed-off-by: Yan Markman <ymarkman@...vell.com>
> ---
>  drivers/net/ethernet/marvell/mvpp2.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvpp2.c b/drivers/net/ethernet/marvell/mvpp2.c
> index 55300b1fe6c0..1a893ef70eab 100644
> --- a/drivers/net/ethernet/marvell/mvpp2.c
> +++ b/drivers/net/ethernet/marvell/mvpp2.c
> @@ -498,7 +498,7 @@
>   * skb. As we need a maxium of two descriptors per fragments (1 header, 1 data),
>   * multiply this value by two to count the maximum number of skb descs needed.
>   */
> -#define MVPP2_MAX_TSO_SEGS		300
> +#define MVPP2_MAX_TSO_SEGS		100
>  #define MVPP2_MAX_SKB_DESCS		(MVPP2_MAX_TSO_SEGS * 2 + MAX_SKB_FRAGS)
>  
>  /* Dfault number of RXQs in use */
> @@ -5810,7 +5810,7 @@ static int mvpp2_txq_init(struct mvpp2_port *port,
>  		txq_pcpu->tso_headers = NULL;
>  
>  		txq_pcpu->stop_threshold = txq->size - MVPP2_MAX_SKB_DESCS;
> -		txq_pcpu->wake_threshold = txq_pcpu->stop_threshold / 2;
> +		txq_pcpu->wake_threshold = txq_pcpu->stop_threshold - 100;
>  

This number 100 is a magic constant.  If it is related to
MVPP2_MAX_TSO_SEGS, please use that define.  Otherwise
define a new one which is descriptive.

Thank you.