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

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Message-ID: <fd788395-c936-49cf-a85d-d39d1d055131@gmail.com>
Date: Fri, 7 Jun 2024 10:53:55 +0300
From: Tariq Toukan <ttoukan.linux@...il.com>
To: Joe Damato <jdamato@...tly.com>, Jakub Kicinski <kuba@...nel.org>,
 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 07/06/2024 4:02, Joe Damato wrote:
> 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:
> 

Right, currently there's no consistency between the PTP RX/TX 
accountment in real_num_queues.
I don't want to create more work for you, but IMO in the longterm I 
should follow it up with a patch that adds PTP-RX to real_num_rx_queues.

> 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++) {

Do not take num_tc from here, this ptp memory might not exist at this point.
Calculate it the regular way with max_opened_tc.

>           tx->packets += ...ptp_stats.sq[tc].packets;
>           tx->bytes += ...ptp_stats.sq[tc].bytes;
>        }
>    }
> 
> Right? Or am I just way off here?