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

["Alexandre Courbot" <acourbot@nvidia.com>]

On Wed Nov 12, 2025 at 3:42 AM JST, Lyude Paul wrote:
> On Mon, 2025-11-10 at 10:16 -0500, 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 agree. FWIW, it's worth noting that honestly avoiding logging is the way to
> go for anything spammy. I've seen quite a number of heisenbugs that only
> appear when trace logging isn't turned on in nouveau or vice-versa (igt tests
> that fail because logging causes things to time out…).

+1 for tracing, when debugging we are typically interested in a very
small subset of the debug logs and the ability to only enable what is
needed is essential.

Though I am not sure about the current state of tracing support in
Rust...