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: <20220425214928.2aac3391@gandalf.local.home>
Date:   Mon, 25 Apr 2022 21:49:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Luck, Tony" <tony.luck@...el.com>
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

On Mon, 25 Apr 2022 16:49:35 +0000
"Luck, Tony" <tony.luck@...el.com> wrote:

> 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?

Yes, they are expensive as each TRACE_EVENT() can add a few KB of text and
data. But you can add a DECLARE_EVENT_CLASS() and then add "printk"
differences that are less memory heavy.

See DEFINE_EVENT_PRINT().

-- Steve