linux-kernel - Re: [PATCH v2 08/12] nova-core: sequencer: Add register opcodes

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Message-ID: <b07b21e8-5dd4-4d40-bcad-dd8dc4fbaef4@nvidia.com>
Date: Mon, 10 Nov 2025 10:16:45 -0500
From: Joel Fernandes <joelagnelf@...dia.com>
To: Timur Tabi <ttabi@...dia.com>, John Hubbard <jhubbard@...dia.com>
Cc: "dakr@...nel.org" <dakr@...nel.org>, "lossin@...nel.org"
 <lossin@...nel.org>, "ojeda@...nel.org" <ojeda@...nel.org>,
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 Alexandre Courbot <acourbot@...dia.com>,
 "joel@...lfernandes.org" <joel@...lfernandes.org>,
 Alistair Popple <apopple@...dia.com>, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 08/12] nova-core: sequencer: Add register opcodes

really +Steve Rostedt this time.

On 11/10/2025 10:16 AM, Joel Fernandes wrote:
> On 11/5/2025 6:19 PM, Timur Tabi wrote:
>> On Wed, 2025-11-05 at 13:55 -0800, John Hubbard wrote:
>>>> #define nvdev_trace(d,f,a...) nvdev_printk((d), TRACE,   info, f, ##a)
>>>> #define nvdev_spam(d,f,a...)  nvdev_printk((d),  SPAM,    dbg, f, ##a)
>>>
>>> ...and those are unusable, unfortunately. I've tried.
>>
>> This works great for me:
>>
>> modprobe nouveau dyndbg="+p" modeset=1 debug="gsp=spam" config=NvGspRm=1
>>
>> I get all sequencer messages when I boot with these options.
>>
>>> ftrace/bpftrace, maybe those are the real way to "trace"...or something
>>> other than this.
>>
>> You could say the same thing about most dev_dbg() statements.
>>
>> I agree that dev_dbg for sequencer commands is excessive, and that implementing new debug levels
>> just to get sequencer prints is also excessive.  But Nouveau implement nvkm_trace for a reason.  And
>> we all know that because of ? in Rust, NovaCore does a terrible job at telling us where an error
>> actually occurred.  So there is a lot of room for improvement.
> 
> IMO, the best way to do this is the tracing subsystem. It is the lowest overhead
> runtime kernel logging system that I know off, lockless, independent of the
> serial console etc, next to no runtime overhead when off, etc.
> 
> I recommend we use the tracing subsystem for "trace" and even "spam" level
> logging levels for Nova. The brave souls can always ask the tracing subsystem to
> also spam to kernel logs if they so wish.
> 
> ++ Tracing Czar Steven Rostedt as well. Steve, Nova is a new modern Nvidia GPU
> driver.
> 
> I guess we have to decide how to do this - what kind of tracepoints do we need
> for Nova. One use case that just came up is RPC message buffer dumps for
> debugging communication with the firmware.
> 
> thanks,
> 
>  - Joel
>