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

Luck, Tony
2022-04-21T04:26:53Z

>> +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