netdev - Re: [PATCH iwl-next] igc: Get rid of spurious interrupts

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Date: Thu, 13 Jun 2024 08:24:26 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc: Kurt Kanzenbach <kurt@...utronix.de>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [PATCH iwl-next] igc: Get rid of spurious interrupts

On 2024-06-12 12:49:21 [-0700], Vinicius Costa Gomes wrote:
> > diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
> > index 305e05294a26..e666739dfac7 100644
> > --- a/drivers/net/ethernet/intel/igc/igc_main.c
> > +++ b/drivers/net/ethernet/intel/igc/igc_main.c
> > @@ -5811,11 +5815,23 @@ static void igc_watchdog_task(struct work_struct *work)
> >  	if (adapter->flags & IGC_FLAG_HAS_MSIX) {
> >  		u32 eics = 0;
> >  
> > -		for (i = 0; i < adapter->num_q_vectors; i++)
> > -			eics |= adapter->q_vector[i]->eims_value;
> > -		wr32(IGC_EICS, eics);
> > +		for (i = 0; i < adapter->num_q_vectors; i++) {
> > +			struct igc_ring *rx_ring = adapter->rx_ring[i];
> > +
> > +			if (test_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags)) {
> 
> Minor and optional: I guess you can replace test_bit() -> clear_bit()
> with __test_and_clear_bit() here and below.

That are two steps, first test+clear is merged into one and then __ is
added. The former is doable but it will always lead to a write operation
while in the common case the flag isn't set so it will be skipped.
Adding the __ leads to an unlocked operation and I don't see how this is
synchronized against the other writes. In fact, nobody else is doing it.

Sebastian