linux-kernel - Re: [PATCH net v2] net: xilinx: axienet: Fix packet counting

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Message-ID: <20240910073956.53278ffe@kernel.org>
Date: Tue, 10 Sep 2024 07:39:56 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Radhey Shyam Pandey <radhey.shyam.pandey@....com>, "David S . Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, netdev@...r.kernel.org, Michal Simek
 <michal.simek@....com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Andy Chiu <andy.chiu@...ive.com>, Daniel
 Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH net v2] net: xilinx: axienet: Fix packet counting

On Tue, 10 Sep 2024 10:24:36 -0400 Sean Anderson wrote:
> > why are you doing this? To make sure drivers doesn't complete more 
> > than "budget" Tx skbs? The budget is really for Rx, for Tx you can
> > use a reasonable fixed value, independent of what budget core
> > passes in, e.g. 128. See:
> > https://www.kernel.org/doc/html/next/networking/napi.html#datapath-api  
> 
> I read this but it was unclear to me because it seems oriented towards
> "combined" NAPI instances, while we have separate instances for RX and
> TX. So even for TX-only instances, we can ignore budget?

Yes, combined or dedicated it should still reap completions regardless
of budget.

> > Moving this chunk into axienet_free_tx_chain() is a noop, right?
> > Please avoid code cleanups in fixes.  
> 
> The relevant variable (number of descriptors handled) is no longer
> returned to axienet_tx_poll, so it can't update the current descriptor
> properly.

Got it, worth mentioning in the commit msg.