RE: [PATCH v4 09/10] trace: platform/x86/intel/ifs: Add trace point to track Intel IFS operations

From: Luck, Tony
Date: Mon Apr 25 2022 - 12:49:48 EST

> > Add tracing support which may be useful for debugging systems that fail to complete
> > In Field Scan tests.
> >
> > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> > ---
> > drivers/platform/x86/intel/ifs/runtest.c | 5 ++++
> > include/trace/events/intel_ifs.h | 38 ++++++++++++++++++++++++
> From the tracing POV:
> Acked-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>

Question for the future of this driver. There are a couple more scan tools coming
in the future. The interface is similar:

WRMSR to start a scan
RDMSR to get the results

For this first one, I made the trace code do some user friendly decoding of the
WRMSR value to just show the two interesting fields (start & stop).

The future scan modes will have different fields.

I see two paths:

1) Create a new user friendly trace point for each new scan mode.
2) Just provide a generic one that dumps both the 64-bit WRMSR and RDMSR values.

Q: Are trace points "expensive" in some way ... so better to just have one than three?
Or are the cheap enough that decoding for the user is an OK thing?