Subject: Re: [PATCH net-next] eth: mlx5: link NAPI instances to queues and IRQs

From: Joe Damato <[email-masked]>
Date: Mon, 5 Feb 2024 18:51:54 -0800

On Mon, Feb 05, 2024 at 06:38:41PM -0800, Rahul Rameshbabu wrote:
> On Mon, 05 Feb, 2024 17:56:58 -0800 Joe Damato <[email-masked]> wrote:
> > On Mon, Feb 05, 2024 at 05:44:27PM -0800, Rahul Rameshbabu wrote:
> >> 
> >> On Mon, 05 Feb, 2024 17:41:52 -0800 Joe Damato <[email-masked]> wrote:
> >> > On Mon, Feb 05, 2024 at 05:33:39PM -0800, Rahul Rameshbabu wrote:
> >> >> 
> >> >> On Mon, 05 Feb, 2024 17:32:47 -0800 Joe Damato <[email-masked]> wrote:
> >> >> > On Mon, Feb 05, 2024 at 05:09:09PM -0800, Rahul Rameshbabu wrote:
> >> >> >> On Tue, 06 Feb, 2024 01:03:11 +0000 Joe Damato <[email-masked]> wrote:
> >> >> >> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> >> >> >> > index c8e8f512803e..e1bfff1fb328 100644
> >> >> >> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> >> >> >> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> >> >> >> > @@ -2473,6 +2473,9 @@ static void mlx5e_close_queues(struct mlx5e_channel *c)
> >> >> >> >  	mlx5e_close_tx_cqs(c);
> >> >> >> >  	mlx5e_close_cq(&c->icosq.cq);
> >> >> >> >  	mlx5e_close_cq(&c->async_icosq.cq);
> >> >> >> > +
> >> >> >> > +	netif_queue_set_napi(c->netdev, c->ix, NETDEV_QUEUE_TYPE_TX, NULL);
> >> >> >> > +	netif_queue_set_napi(c->netdev, c->ix, NETDEV_QUEUE_TYPE_RX, NULL);
> >> >> >> 
> >> >> >> This should be set to NULL *before* actually closing the rqs, sqs, and
> >> >> >> related cqs right? I would expect these two lines to be the first ones
> >> >> >> called in mlx5e_close_queues. Btw, I think this should be done in
> >> >> >> mlx5e_deactivate_channel where the NAPI is disabled.
> >> >> >> 
> >> >> >> >  }
> >> >> >> >  
> >> >> >> >  static u8 mlx5e_enumerate_lag_port(struct mlx5_core_dev *mdev, int ix)
> >> >> >> > @@ -2558,6 +2561,7 @@ static int mlx5e_open_channel(struct mlx5e_priv *priv, int ix,
> >> >> >> >  	c->stats    = &priv->channel_stats[ix]->ch;
> >> >> >> >  	c->aff_mask = irq_get_effective_affinity_mask(irq);
> >> >> >> >  	c->lag_port = mlx5e_enumerate_lag_port(priv->mdev, ix);
> >> >> >> > +	c->irq		= irq;
> >> >> >> >  
> >> >> >> >  	netif_napi_add(netdev, &c->napi, mlx5e_napi_poll);
> >> >> >> >  
> >> >> >> > @@ -2602,6 +2606,10 @@ static void mlx5e_activate_channel(struct mlx5e_channel *c)
> >> >> >> >  		mlx5e_activate_xsk(c);
> >> >> >> >  	else
> >> >> >> >  		mlx5e_activate_rq(&c->rq);
> >> >> >> > +
> >> >> >> > +	netif_napi_set_irq(&c->napi, c->irq);
> >> >> 
> >> >> One small comment that I missed in my previous iteration. I think the
> >> >> above should be moved to mlx5e_open_channel right after netif_napi_add.
> >> >> This avoids needing to save the irq in struct mlx5e_channel.
> >> >
> >> > I couldn't move it to mlx5e_open_channel because of how safe_switch_params
> >> > and the mechanics around that seem to work (at least as far as I could
> >> > tell).
> >> >
> >> > mlx5 seems to create a new set of channels before closing the previous
> >> > channel. So, moving this logic to open_channels and close_channels means
> >> > you end up with a flow like this:
> >> >
> >> >   - Create new channels (NAPI netlink API is used to set NAPIs)
> >> >   - Old channels are closed (NAPI netlink API sets NULL and overwrites the
> >> >     previous NAPI netlink calls)
> >> >
> >> > Now, the associations are all NULL.
> >> >
> >> > I think moving the calls to active / deactivate fixes that problem, but
> >> > requires that irq is stored, if I am understanding the driver correctly.
> >> 
> >> I believe moving the changes to activate / deactivate channels resolves
> >> this problem because only one set of channels will be active, so you
> >> will no longer have dangling association conflicts for the queue ->
> >> napi. This is partially why I suggested the change in that iteration.
> >
> > As far as I can tell, it does.
> >  
> >> As for netif_napi_set_irq, that alone can be in mlx5e_open_channel (that
> >> was the intention of my most recent comment. Not that all the other
> >> associations should be moved as well). I agree that the other
> >> association calls should be part of activate / deactivate channels.
> >
> > OK, sure that makes sense. I make that change, too.
> >
> 
> Also for your v2, it would be great if you can use the commit message
> subject 'net/mlx5e: link NAPI instances to queues and IRQs' rather than
> 'eth: mlx5: link NAPI instances to queues and IRQs'.

Didn't see this before I sent it. If it matters that much, I can send a v3
with an updated commit message.