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From:   "Luck, Tony" <tony.luck@intel.com>
To:     Steven Rostedt <rostedt@goodmis.org>
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Subject: RE: [PATCH v3 10/11] trace: platform/x86/intel/ifs: Add trace point
 to track Intel IFS operations
Thread-Topic: [PATCH v3 10/11] trace: platform/x86/intel/ifs: Add trace point
 to track Intel IFS operations
Thread-Index: AQHYVAv/GMu0aAF5oU2sc2NlODgUPKz57MaA///Yp0A=
Date:   Thu, 21 Apr 2022 04:26:39 +0000
Message-ID: <adc49af263e2464f86b20ccc2d8f184d@intel.com>
References: <20220407191347.9681-1-jithu.joseph@intel.com>
        <20220419163859.2228874-1-tony.luck@intel.com>
        <20220419163859.2228874-11-tony.luck@intel.com>
 <20220420193839.6e9d810b@gandalf.local.home>
In-Reply-To: <20220420193839.6e9d810b@gandalf.local.home>
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>> +TRACE_EVENT(ifs_status,
>> +
>> +	TP_PROTO(union ifs_scan activate, union ifs_status status),
>
> Really, you want to pass the structure in by value, so that we have two
> copies? One to get to this function and then one to write to the ring
> buffer?

These "structures" are just bitfield helpers for a u64 that is passed into
WRMSR (in the case of activate) and received back from RDMSR in
the case of status.

So this is really just a pair of u64 arguments, with the compiler handling
the bit field extractions into the ring buffer.

Here are the definitions:

union ifs_scan {
        u64     data;
        struct {
                u32     start   :8;
                u32     stop    :8;
                u32     rsvd    :16;
                u32     delay   :31;
                u32     sigmce  :1;
        };
};

union ifs_status {
        u64     data;
        struct {
                u32     chunk_num               :8;
                u32     chunk_stop_index        :8;
                u32     rsvd1                   :16;
                u32     error_code              :8;
                u32     rsvd2                   :22;
                u32     control_error           :1;
                u32     signature_error         :1;
        };
};

Would it be better to do the bit extractions of the start/stop fields first=
?

-Tony