linux-kernel - Re: [RFC 10/10] trace: platform/x86/intel/ifs: Add trace point to track Intel IFS operations

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Date:   Tue, 1 Mar 2022 17:02:14 -0800
From:   "Joseph, Jithu" <jithu.joseph@...el.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     <hdegoede@...hat.com>, <markgross@...nel.org>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
        <corbet@....net>, <gregkh@...uxfoundation.org>,
        <andriy.shevchenko@...ux.intel.com>, <ashok.raj@...el.com>,
        <tony.luck@...el.com>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <platform-driver-x86@...r.kernel.org>,
        <patches@...ts.linux.dev>, <ravi.v.shankar@...el.com>
Subject: Re: [RFC 10/10] trace: platform/x86/intel/ifs: Add trace point to
 track Intel IFS operations



On 3/1/2022 12:17 PM, Steven Rostedt wrote:
> On Tue,  1 Mar 2022 11:54:57 -0800
> Jithu Joseph <jithu.joseph@...el.com> wrote:
> 
>> +	TP_STRUCT__entry(
>> +		__field(	u8,	start	)
>> +		__field(	u8,	stop	)
>> +		__field(	u64,	status	)
>> +	),
> 
> I'd suggest swapping this to:
> 
> 		__field(	u64,	status	)
> 		__field(	u8,	start	)
> 		__field(	u8,	stop	)
> 
> As trace events are usually aligned by 4 bytes (sometimes 8 for archs that
> require 8byte alignment for 8 byte words), but any event, putting the
> padding at the end of the event is better than in the middle of the event.
> 
> Having the u64 come after two u8 (two byes) will pretty much guarantee a 6
> bytes hole in the middle of the event.

Will reorder the fields as you suggested. Appreciate the detailed comment.

Jithu