Re: [RFC net-next v4 2/2] net/mlx5e: Add per queue netdev-genl stats

[Joe Damato <jdamato@fastly.com>]

On Thu, Jun 06, 2024 at 05:19:42PM -0700, Jakub Kicinski wrote:
> On Thu, 6 Jun 2024 14:54:40 -0700 Joe Damato wrote:
> > > > Compare the values in /proc/net/dev match the output of cli for the same
> > > > device, even while the device is down.
> > > > 
> > > > Note that while the device is down, per queue stats output nothing
> > > > (because the device is down there are no queues):  
> > > 
> > > This part is not true anymore.  
> > 
> > It is true with this patch applied and running the command below.
> > Maybe I should have been more explicit that using cli.py outputs []
> > when scope = queue, which could be an internal cli.py thing, but
> > this is definitely true with this patch.
> > 
> > Did you test it and get different results?
> 
> To avoid drivers having their own interpretations what "closed" means,
> core hides all queues in closed state:
> 
> https://elixir.bootlin.com/linux/v6.10-rc1/source/net/core/netdev-genl.c#L582
> 
> > > PTP RQ index is naively assigned to zero:
> > > rq->ix           = MLX5E_PTP_CHANNEL_IX;
> > > 
> > > but this isn't to be used as the stats index.
> > > Today, the PTP-RQ has no matcing rxq in the kernel level.
> > > i.e. turning PTP-RQ on won't add a kernel-level RXQ to the
> > > real_num_rx_queues.
> > > Maybe we better do.
> > > If not, and the current state is kept, the best we can do is let the PTP-RQ
> > > naively contribute its queue-stat to channel 0.  
> > 
> > OK, it sounds like the easiest thing to do is just count PTP as
> > channel 0, so if i == 0, I'll in the PTP stats.
> > 
> > But please see below regarding testing whether or not PTP is
> > actually enabled or not.
> 
> If we can I think we should avoid making queue 0 too special. 
> If someone configures steering and only expects certain packets on
> queue 0 - getting PTP counted there will be a surprise. 
> I vote to always count it towards base.

I'm OK with reporting PTP RX in base and only in base.

But, that would then leave PTP TX:

PTP TX stats are reported in mlx5e_get_queue_stats_tx because
the user will pass in an 'i' which refers to the PTP txq. This works
fine with the mlx5e_get_queue_stats_tx code as-is because the PTP
txqs are mapped in the new priv->txq2sq_stats array.

However.... if PTP is enabled and then disabled by the user, that
leaves us in this state:

  priv->tx_ptp_opened && !test_bit(MLX5E_PTP_STATE_TX, channels.ptp->state) 

e.g. PTP TX was opened at some point but is currently disabled as
the bit is unset.

In this case, when the txq2sq_stats map is built, it'll exclude PTP
stats struct from that mapping if MLX5E_PTP_STATE_TX is not set.

So, in this case, the stats have to be reported in base with
something like this (psuedo code):
 
  if (priv->tx_ptp_opened &&
     ! test_bit(MLX5E_PTP_STATE_TX, channels.ptp->state)) {
      for (tc = 0; tc < priv->channels.ptp->num_tc; tc++) {
         tx->packets += ...ptp_stats.sq[tc].packets;
         tx->bytes += ...ptp_stats.sq[tc].bytes;
      }
  }

Right? Or am I just way off here?