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

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Message-ID: <20251110115905.68bd2826@gandalf.local.home>
Date: Mon, 10 Nov 2025 11:59:05 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Joel Fernandes <joelagnelf@...dia.com>
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Subject: Re: [PATCH v2 08/12] nova-core: sequencer: Add register opcodes

On Mon, 10 Nov 2025 10:16:45 -0500
Joel Fernandes <joelagnelf@...dia.com> wrote:

> > 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.

Not sure if there was a question here, but you can enable tracing via the
kernel command line and it will record into the ring buffer, and read it
out via /sys/kernel/tracing/trace. You could also create instances by the
kernel command line that will place events in different ring buffer
instances (/sys/kernel/tracing/instances/<instance>/trace). You could even
filter the events based on the trace event fields, process ID, CPU, etc.

There's also a tp_printk kernel command line option that will turn every
trace event into a printk() statement. You need to be careful of what
events you enable when doing this, as some events (like locking events) can
live lock the system if they are piped to printk().

After boot up, you can turn off the tp_printk with:

  echo 0 > /proc/sys/kernel/tracepoint_printk

-- Steve

> > 
> > 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.