netdev - Re: [PATCH net-next 4/4] net: stmmac: Always use TX coalesce timer value when rescheduling

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Date:   Sat, 14 Dec 2019 12:28:37 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>
Cc:     netdev@...r.kernel.org, Joao Pinto <Joao.Pinto@...opsys.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 4/4] net: stmmac: Always use TX coalesce timer
 value when rescheduling

On Tue, 10 Dec 2019 20:54:44 +0100, Jose Abreu wrote:
> When we have pending packets we re-arm the TX timer with a magic value.
> Change this from the hardcoded value to the pre-defined TX coalesce
> timer value.

s/pre-defined/user controlled/ ?

> Signed-off-by: Jose Abreu <Jose.Abreu@...opsys.com>
> ---
> Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
> Cc: Alexandre Torgue <alexandre.torgue@...com>
> Cc: Jose Abreu <joabreu@...opsys.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Maxime Coquelin <mcoquelin.stm32@...il.com>
> Cc: netdev@...r.kernel.org
> Cc: linux-stm32@...md-mailman.stormreply.com
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index f61780ae30ac..726a17d9cc35 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -1975,7 +1975,7 @@ static int stmmac_tx_clean(struct stmmac_priv *priv, int budget, u32 queue)
>  
>  	/* We still have pending packets, let's call for a new scheduling */
>  	if (tx_q->dirty_tx != tx_q->cur_tx)
> -		mod_timer(&tx_q->txtimer, STMMAC_COAL_TIMER(10));
> +		mod_timer(&tx_q->txtimer, STMMAC_COAL_TIMER(priv->tx_coal_timer));

I think intent of this code is to re-check the ring soon. The same
value of 10 is used in stmmac_tx_timer() for quick re-check.

tx_coal_timer defaults to 1000, so it's quite a jump from 10 to 1000.

I think the commit message leaves too much unsaid.

Also if you want to change to the ethtool timeout value, could you move 
stmmac_tx_timer_arm() and reuse that helper?

>  
>  	__netif_tx_unlock_bh(netdev_get_tx_queue(priv->dev, queue));
>