RE: [PATCH v3 10/11] trace: platform/x86/intel/ifs: Add trace point to track Intel IFS operations

[Luck, Tony]

>> +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