netdev - Re: [PATCH net-next] amd-xgbe: schedule NAPI on Rx Buffer Unavailable to prevent RX stalls

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Message-ID: <20251128103853.3e6f7996@kernel.org>
Date: Fri, 28 Nov 2025 10:38:53 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: "Rangoju, Raju" <raju.rangoju@....com>
Cc: netdev@...r.kernel.org, pabeni@...hat.com, edumazet@...gle.com,
 davem@...emloft.net, andrew+netdev@...n.ch, Shyam-sundar.S-k@....com
Subject: Re: [PATCH net-next] amd-xgbe: schedule NAPI on Rx Buffer
 Unavailable to prevent RX stalls

On Fri, 28 Nov 2025 11:20:09 +0530 Rangoju, Raju wrote:
> > On Mon, 24 Nov 2025 15:41:11 +0530 Raju Rangoju wrote:  
> >> When Rx Buffer Unavailable (RBU) interrupt is asserted, the device can
> >> stall under load and suffer prolonged receive starvation if polling is
> >> not initiated. Treat RBU as a wakeup source and schedule the appropriate
> >> NAPI instance (per-channel or global) to promptly recover from buffer
> >> shortages and refill descriptors.  
> > 
> > You need to say more.. Under heavy load network devices will routinely
> > run out of Rx buffers, it's expected if Rx processing is slower than
> > the network. What hw condition and scenario exactly are you describing
> > here?  
> 
> During the bi-directional traffic device is running out of RX buffers, 
> it could be because of slower rx processing. HW notifies this via Rx 
> Buffer Unavailable (RBU) interrupt. What is being described above is 
> that, driver should treat RBU interrupt as source to trigger the NAPI 
> poll immediately, rather than waiting for regular rx interrupts to 
> process the rx buffers.

Ack, all I'm saying is that the commit message seems to be overselling
the impact of this change. Patch is very very unlikely to make anything
more "prompt". 99% of the time if Rx buffers are not refilled we are
either in OOM or Rx overload, so either we won't be able to alloc the
buffers, or NAPI is already scheduled. But of course trying to schedule
the NAPI does seem like the more correct reaction, in case we missed an
IRQ or such. Maybe rephrase a little.. unless there's some magic here
im not aware of