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

["Nazle Asmade, Muhammad Nazim Amirul" <muhammad.nazim.amirul.nazle.asmade@altera.com>]

On 4/6/2026 5:08 pm, Maxime Chevallier wrote:
> Hi,
> 
>>> 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
>>>
>> Hi Maxime,
>>
>> Thank you for the review and for pointing out the rx_buf_unav_irq concern.
>>
>> We do have interrupt storm data to share. On Agilex5, under heavy RX
>> pressure we observed:
>>
>> Under heavy RX pressure we observed eth0:mac firing 1,821,811,555 times
>> vs 2,618,627 actual RX completions on eth0:rx-0 — a ~695x ratio.
> 
> Ouch indeed. The stat itself has to stay, but the behaviour of that
> counter is already different depending on the DWMAC core version.
> 
> I think we can get this patch in, but please state in the commit message
> the performance measurements you're mentioning, as well as the fact
> that the counter will now always show at 0 on XGMAC2 devices.
> 
> Maybe we'll eventually need some switch to toggle these counters, as it's
> some valuable information when debugging, but has a significant impact on
> speeds.
> 
> With the commit log updates,
> 
> Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> 
>>
>> BR,
>> Nazim
> 
Hi Maxime,

Thanks for your review! Commit message now updated in v2
https://lore.kernel.org/all/20260604094512.21243-1-muhammad.nazim.amirul.nazle.asmade@altera.com/

BR,
Nazim