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

[Andrew Lunn <andrew@lunn.ch>]

On Sun, May 24, 2026 at 11:16:53PM -0700, muhammad.nazim.amirul.nazle.asmade@altera.com wrote:
> From: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade@altera.com>
> 
> Currently hrtimer_start is called even if hrtimer is
> active. This is unnecessary and expensive in some targets.
> This patch avoids calling hrtimer_start unnecessarily.
> 
> Signed-off-by: Rohan G Thomas <rohan.g.thomas@intel.com>
> Signed-off-by: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade@altera.com>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> 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
> +	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);

Is there a race condition here? I've not thought about it enough to
know if there is/is not.

Also, does this change the meaning of tx_coal_timer?

I think the commit message needs expanding, to cover these issues. For
performance changes, it is also normal to include some performance
numbers, before/after, in the commit message.

    Andrew

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