[Intel-wired-lan] [PATCH iwl-net 2/2] idpf: trigger SW interrupt when exiting wb_on_itr mode

[Singh, Krishneil K]

> -----Original Message-----
> From: Hay, Joshua A <joshua.a.hay at intel.com>
> Sent: Tuesday, December 3, 2024 9:53 AM
> To: Lobakin, Aleksander <aleksander.lobakin at intel.com>
> Cc: intel-wired-lan at lists.osuosl.org; Kitszel, Przemyslaw
> <przemyslaw.kitszel at intel.com>; Kubiak, Michal <michal.kubiak at intel.com>;
> Chittim, Madhu <madhu.chittim at intel.com>; netdev at vger.kernel.org
> Subject: RE: [Intel-wired-lan][PATCH iwl-net 2/2] idpf: trigger SW interrupt
> when exiting wb_on_itr mode
> 
> > From: Lobakin, Aleksander <aleksander.lobakin at intel.com>
> > Cc: intel-wired-lan at lists.osuosl.org; Kitszel, Przemyslaw
> > <przemyslaw.kitszel at intel.com>; Kubiak, Michal
> <michal.kubiak at intel.com>;
> > Chittim, Madhu <madhu.chittim at intel.com>; netdev at vger.kernel.org
> > Subject: Re: [Intel-wired-lan][PATCH iwl-net 2/2] idpf: trigger SW interrupt
> > when exiting wb_on_itr mode
> >
> > From: Joshua Hay <joshua.a.hay at intel.com>
> > Date: Mon, 25 Nov 2024 15:58:55 -0800
> >
> > > There is a race condition between exiting wb_on_itr and completion write
> > > backs. For example, we are in wb_on_itr mode and a Tx completion is
> > > generated by HW, ready to be written back, as we are re-enabling
> > > interrupts:
> > >
> > > 	HW                      SW
> > > 	|                       |
> > > 	|			| idpf_tx_splitq_clean_all
> > > 	|                       | napi_complete_done
> > > 	|			|
> > > 	| tx_completion_wb 	| idpf_vport_intr_update_itr_ena_irq
> > >
> > > That tx_completion_wb happens before the vector is fully re-enabled.
> > > Continuing with this example, it is a UDP stream and the
> > > tx_completion_wb is the last one in the flow (there are no rx packets).
> > > Because the HW generated the completion before the interrupt is fully
> > > enabled, the HW will not fire the interrupt once the timer expires and
> > > the write back will not happen. NAPI poll won't be called.  We have
> > > indicated we're back in interrupt mode but nothing else will trigger the
> > > interrupt. Therefore, the completion goes unprocessed, triggering a Tx
> > > timeout.
> > >
> > > To mitigate this, fire a SW triggered interrupt upon exiting wb_on_itr.
> > > This interrupt will catch the rogue completion and avoid the timeout.
> > > Add logic to set the appropriate bits in the vector's dyn_ctl register.
> > >
> > > Fixes: 9c4a27da0ecc ("idpf: enable WB_ON_ITR")
> > > Reviewed-by: Madhu Chittim <madhu.chittim at intel.com>
> > > Signed-off-by: Joshua Hay <joshua.a.hay at intel.com>
> > > ---
> > >  drivers/net/ethernet/intel/idpf/idpf_txrx.c | 30 ++++++++++++++-------
> > >  1 file changed, 20 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > > index a8989dd98272..9558b90469c8 100644
> > > --- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > > +++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
> > > @@ -3604,21 +3604,32 @@ static void idpf_vport_intr_dis_irq_all(struct


Tested-by: Krishneil Singh <krishneil.k.singh at intel.com>