Re: [PATCH 13/15] perf_counter: provide generic callchain bits

From: Corey Ashford
Date: Wed Apr 01 2009 - 19:30:33 EST


Peter Zijlstra wrote:
On Wed, 2009-04-01 at 14:48 +1100, Paul Mackerras wrote:
Peter Zijlstra writes:

That still has the record and read things separate, but as one unified
overflow output.
I take it PERF_EVENT_OVERFLOW refers to counter overflow, not ring
buffer overflow? That had me confused for a bit, so more explicit
naming, or at least some comments, would be good.

Ah, yes, I see how that can confuse. PERF_EVENT_COUNTER_OVERFLOW then?

I was thinking about doing splice() support and that could also generate
actual event overflow events ;-)

/*
+ * Bits that can be set in hw_event.record_type to request information
+ * in the overflow packets.
+ */
+enum perf_counter_record_format {
+ PERF_RECORD_IP = 1U << 0,
+ PERF_RECORD_TID = 1U << 1,
+ PERF_RECORD_GROUP = 1U << 2,
+ PERF_RECORD_CALLCHAIN = 1U << 3,
+};
[snip]
enum perf_event_type {
- PERF_EVENT_GROUP = 1,
-
- PERF_EVENT_MMAP = 2,
- PERF_EVENT_MUNMAP = 3,
+ PERF_EVENT_MMAP = 1,
+ PERF_EVENT_MUNMAP = 2,
PERF_EVENT_OVERFLOW = 1UL << 31,
__PERF_EVENT_IP = 1UL << 30,
__PERF_EVENT_TID = 1UL << 29,
- __PERF_EVENT_CALLCHAIN = 1UL << 28,
+ __PERF_EVENT_GROUP = 1UL << 28,
+ __PERF_EVENT_CALLCHAIN = 1UL << 27,
Could we use the same value (and even the same name) for
PERF_RECORD_IP/__PERF_EVENT_IP, PERF_RECORD_TID/__PERF_EVENT_TID,
etc.?

I suppose we could.

Also, I haven't looked at the callchain stuff much, but does the
callchain info contain a recognizable end delimiter? At present the
callchain comes last, but if we add more output elements they'll
presumably go after it, so working out where the callchain ends may
become tricky if we're not careful.

It writes:

struct callchain_event {
u64 nr
u64 ips[nr]
};

Looking at the current version of perf_counter.h in the -tip tree, this struct definition is not visible to userspace (it's in the #ifdef KERNEL section).

- Corey

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