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

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Message-ID: <20251126191342.6728250d@kernel.org>
Date: Wed, 26 Nov 2025 19:13:42 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Raju Rangoju <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 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?

>  		dma_ch_isr = XGMAC_DMA_IOREAD(channel, DMA_CH_SR);
> +		/* Precompute flags once */
> +		ti  = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, TI);
> +		ri  = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, RI);
> +		rbu = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, RBU);
> +		fbe = !!XGMAC_GET_BITS(dma_ch_isr, DMA_CH_SR, FBE);

Please split this into two patches, one pure refactoring with no
functional changes and second one changing RBU handling.

> +		if (rbu) {
> +			schedule_napi = true;
> +			pdata->ext_stats.rx_buffer_unavailable++;
> +			netif_dbg(pdata, intr, pdata->netdev,
> +				  "RBU on DMA_CH %u, scheduling %s NAPI\n",
> +				  i, per_ch_irq ? "per-channel" : "global");

I guess it's just _dbg() but as a general rule when the system is under
overload printing stuff (potentially over UART) is the last thing you
should be doing. How is this print useful to you?
-- 
pw-bot: cr