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

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Message-ID: <1752057af33e4eb28bcea0fd75e44048@intel.com>
Date:   Mon, 25 Apr 2022 16:49:35 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "markgross@...nel.org" <markgross@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "corbet@....net" <corbet@....net>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "Joseph, Jithu" <jithu.joseph@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: RE: [PATCH v4 09/10] trace: platform/x86/intel/ifs: Add trace point
 to track Intel IFS operations

> > 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@...el.com>
> > Signed-off-by: Tony Luck <tony.luck@...el.com>
> > ---
> >  MAINTAINERS                              |  1 +
> >  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@...dmis.org>

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?

Thanks

-Tony