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

From: Jakub Kicinski <redacted>
Date: Dec/14/2019, 20:28:37 (UTC+00:00)

On Tue, 10 Dec 2019 20:54:44 +0100, Jose Abreu wrote:

quoted

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/ ?

quoted

Signed-off-by: Jose Abreu <Jose.Abreu@synopsys.com>
---
Cc: Giuseppe Cavallaro <redacted>
Cc: Alexandre Torgue <redacted>
Cc: Jose Abreu <redacted>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: netdev@vger.kernel.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.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

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