Re: [PATCH] net: stmmac: xgmac2: disable RBUE in default RX interrupt mask

[Maxime Chevallier]

Hi,

On 5/29/26 09:17, muhammad.nazim.amirul.nazle.asmade@xxxxxxxxxx wrote:
> From: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade@xxxxxxxxxx>
>
> Enabling the RX Buffer Unavailable (RBUE) interrupt is counterproductive
> and can trigger a MAC interrupt storm under heavy RX pressure. When the
> DMA runs out of RX descriptors it fires RBUE continuously until software
> refills the ring.
>
> However, RBUE is redundant: the normal RX completion interrupt (RIE)
> already triggers NAPI, which processes completed descriptors and refills
> the ring, causing the DMA to resume. The RBUE handler itself only sets
> handle_rx - the same outcome as RIE.
>
> Remove RBUE from XGMAC_DMA_INT_DEFAULT_EN and XGMAC_DMA_INT_DEFAULT_RX
> to prevent the interrupt storm while keeping normal RX handling intact.
>
> Fixes: d6ddfacd95c7 ("net: stmmac: Add DMA related callbacks for XGMAC2")
> Signed-off-by: Nazim Amirul <muhammad.nazim.amirul.nazle.asmade@xxxxxxxxxx>

We had an opposite discussion about enabling rx buf unavailable
interrupts for other DWMAC versions :

https://lore.kernel.org/netdev/E1wBBaR-0000000GZHR-1dbM@xxxxxxxxxxxxxxxxxxxxxx/

While your patch makes sense, I think it's important to note that it'll
now make the "rx_buf_unav_irq" stat (that we can query from userspace)
stuck at 0 now.

That's a user-visible behaviour change, for a stat that can be useful,
one could consider that a uAPI change...

Do you have some numbers on the perf impact you see when buffer
starvation hits to see what we are gaining/losing here ?

Maxime