On Thu, 2009-04-02 at 18:46 -0700, Corey Ashford wrote:Currently, perf_counter has the ability to record the following on event counter overflow:
Instruction Pointer
Call chain
Group counter values
Thread id
To give perf_counter similar capabilities to perfmon2's default sampling module, I'd like the following additional sample data to be added.
Time stamp
Rather hard actually, to provide a decent timestamp from NMI context.
CPU number
Could do I guess.
Thread Group Id
As in the process id? PERF_RECORD_TID already provides that.
I'd suggest the following
enum perf_counter_record_format {
PERF_RECORD_IP = 1U << 0,
PERF_RECORD_TID = 1U << 1,
PERF_RECORD_TGID = 1U << 2,
- PERF_RECORD_GROUP = 1U << 2,
+ PERF_RECORD_GROUP = 1U << 3,
- PERF_RECORD_CALLCHAIN = 1U << 3,
+ PERF_RECORD_CALLCHAIN = 1U << 4,
+ PERF_RECORD_CPU_ID = 1U << 5,
+ PERF_RECORD_TIMESTAMP = 1U << 6,
};
And of course the obvious changes to perf_event_type.
I would expect that CPU ID would be 32 bits, and the timestamp to be the 64-bit current time. TGID is the same size as TID.
Right, so PREF_RECORD_TID provides:
{ u32 pid, tid; }
PERF_RECORD_TIMESTAMP would provide something like:
{ u64 time; }
and per our u64 alignment rule, PERF_RECORD_CPU would provide
{ u64 cpuid; }
unless you can think of anything else to stuff in there?
I am guessing the only difficult thing here would be obtaining the current time from an IRQ, especially NMI handler. Is this difficult?
Yes, quite :-) I'll have to see what we can do there -- we could do a
best effort thing with little to no guarantees I think.