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

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Date: Thu, 6 Jun 2024 17:19:42 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Joe Damato <jdamato@...tly.com>
Cc: Tariq Toukan <ttoukan.linux@...il.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, nalramli@...tly.com, Saeed Mahameed
 <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni
 <pabeni@...hat.com>, Richard Cochran <richardcochran@...il.com>, "open
 list:MELLANOX MLX5 core VPI driver" <linux-rdma@...r.kernel.org>, Tariq
 Toukan <tariqt@...dia.com>
Subject: Re: [RFC net-next v4 2/2] net/mlx5e: Add per queue netdev-genl
 stats

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.