netdev - Re: [PATCH net-next 3/4] net: stmmac: Let TX and RX interrupts be independently enabled/disabled

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Message-ID: <20191216121404.43966b89@cakuba.netronome.com>
Date:   Mon, 16 Dec 2019 12:14:04 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jose Abreu <Jose.Abreu@...opsys.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Ripard <mripard@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 3/4] net: stmmac: Let TX and RX interrupts be
 independently enabled/disabled

On Mon, 16 Dec 2019 09:18:50 +0000, Jose Abreu wrote:
> > > @@ -3759,24 +3777,18 @@ static int stmmac_napi_poll_tx(struct napi_struct *napi, int budget)
> > >  	struct stmmac_channel *ch =
> > >  		container_of(napi, struct stmmac_channel, tx_napi);
> > >  	struct stmmac_priv *priv = ch->priv_data;
> > > -	struct stmmac_tx_queue *tx_q;
> > >  	u32 chan = ch->index;
> > >  	int work_done;
> > >  
> > >  	priv->xstats.napi_poll++;
> > >  
> > > -	work_done = stmmac_tx_clean(priv, DMA_TX_SIZE, chan);
> > > -	work_done = min(work_done, budget);
> > > -
> > > -	if (work_done < budget)
> > > -		napi_complete_done(napi, work_done);
> > > +	work_done = stmmac_tx_clean(priv, budget, chan);
> > > +	if (work_done < budget && napi_complete_done(napi, work_done)) {  
> > 
> > Not really related to this patch, but this looks a little suspicious. 
> > I think the TX completions should all be processed regardless of the
> > budget. The budget is for RX.  
> 
> Well but this is a TX NAPI ... Shouldn't it be limited to prevent CPU 
> starvation ?

It is a bit confusing, but at least netpoll expects the TX completions
to be processed with zero budget. Check out poll_one_napi().