Re: [PATCH v2] net: stmmac: Improve Tx timer arm logic further

[Nazle Asmade, Muhammad Nazim Amirul]

On 28/5/2026 9:58 am, Andrew Lunn wrote:
>> pre-patch behaviour. The meaning of tx_coal_timer is unchanged.
> 
>> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> index 3591755ea30b..35da51c26248 100644
>> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>> @@ -3341,12 +3341,14 @@ static void stmmac_tx_timer_arm(struct stmmac_priv *priv, u32 queue)
>>   	 * Try to cancel any timer if napi is scheduled, timer will be armed
>>   	 * again in the next scheduled napi.
>>   	 */
>> -	if (unlikely(!napi_is_scheduled(napi)))
>> -		hrtimer_start(&tx_q->txtimer,
>> -			      STMMAC_COAL_TIMER(tx_coal_timer),
>> -			      HRTIMER_MODE_REL);
>> -	else
> 
> With this code, the timer is always tx_coal_timer in the future.
> 
> 
>> +	if (unlikely(!napi_is_scheduled(napi))) {
>> +		if (unlikely(!(hrtimer_active(&tx_q->txtimer))))
>> +			hrtimer_start(&tx_q->txtimer,
>> +				      STMMAC_COAL_TIMER(tx_coal_timer),
>> +				      HRTIMER_MODE_REL);
> 
> If the timer is not active, it is set to tx_coal_timer in the
> future. However, if the timer is active, meaning it is already
> counting down, it is left alone, so is less than tx_coal_timer in the
> future.
> 
> Do i have this right?
> 
> Doesn't that change the meaning of the timer. It now actually goes off
> sooner?
> 
> This is somewhat academic. The point of coalescence is to reduce
> overheads. The increase in performance shows that this change does
> reduce overheads.
> 
> 	Andrew
Hi Andrew,

Yes, you have it right. I have updated the commit message in v3 to 
correctly describe this behaviour change.

Thanks, Nazim