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

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Message-ID: <BN8PR12MB3266BDA48CE9F65D564B0918D3510@BN8PR12MB3266.namprd12.prod.outlook.com>
Date:   Mon, 16 Dec 2019 09:20:53 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     "netdev@...r.kernel.org" <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-stm32@...md-mailman.stormreply.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next 4/4] net: stmmac: Always use TX coalesce timer
 value when rescheduling

From: Jakub Kicinski <jakub.kicinski@...ronome.com>
Date: Dec/14/2019, 20:28:37 (UTC+00:00)

> 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?

Yeah, it's a quick re-check but 10us can be too low on some speeds and 
leads to CPU useless-looping. The intent is to let this always be 
configurable by user.

---
Thanks,
Jose Miguel Abreu