linux-kernel - Re: [PATCH V3 5/5] misc: mlx5ctl: Add umem reg/unreg ioctl

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Message-ID: <7ae9adff-5a6a-4ca6-983b-1d866dae9199@kernel.org>
Date:   Tue, 21 Nov 2023 14:18:27 -0800
From:   David Ahern <dsahern@...nel.org>
To:     Saeed Mahameed <saeedm@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Saeed Mahameed <saeed@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Jiri Pirko <jiri@...dia.com>, Leonid Bloch <lbloch@...dia.com>,
        Itay Avraham <itayavr@...dia.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 5/5] misc: mlx5ctl: Add umem reg/unreg ioctl

On 11/21/23 1:04 PM, Saeed Mahameed wrote:
> On 21 Nov 12:44, Jakub Kicinski wrote:
>> On Mon, 20 Nov 2023 23:06:19 -0800 Saeed Mahameed wrote:
>>> high frequency diagnostic counters
>>
>> So is it a debug driver or not a debug driver?
>>
> 
> High frequency _diagnostic_ counters are a very useful tool for
> debugging a high performance chip. So yes this is for diagnostics/debug.
> 
>> Because I'm pretty sure some people want to have access to high freq
>> counters in production, across their fleet. What's worse David Ahern
>> has been pitching a way of exposing device counters which would be
>> common across netdev.
.

For context on the `what's worse ...` comment for those who have not
seen the netconf slides:
https://netdev.bots.linux.dev/netconf/2023/david.pdf

and I am having a hard time parsing Kuba's intent with that comment here
(knowing you did not like the pitch I made at netconf :-))


> 
> This is not netdev, this driver is to support ConnectX chips and SoCs
> with any stack, netdev/rdma/vdpa/virtio and internal chip units and
> acceleration engines, add to that ARM core diagnostics in case of
> Blue-Field DPUs.
> I am not looking for counting netdev ethernet packets in this driver.
> 
> I am also pretty sure David will also want an interface to access other
> than netdev counters, to get more visibility on how a specific chip is
> behaving.

yes, and h/w counters were part of the proposal. One thought is to
leverage userspace registered memory with the device vs mapping bar
space, but we have not moved beyond a theoretical discussion at this point.

> 
>> Definite nack on this patch.
> 
> Based on what ?

It's a generic interface argument?