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perf, x86: use LBR for PEBS IP+1 fixup

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Use the LBR to fix up the PEBS IP+1 issue.

As said, PEBS reports the next instruction, here we use the LBR to find
the last branch and from that construct the actual IP. If the IP matches
the LBR-TO, we use LBR-FROM, otherwise we use the LBR-TO address as the
beginning of the last basic block and decode forward.

Once we find a match to the current IP, we use the previous location.

This patch introduces a new ABI element: PERF_RECORD_MISC_EXACT, which
conveys that the reported IP (PERF_SAMPLE_IP) is the exact instruction
that caused the event (barring CPU errata).

The fixup can fail due to various reasons:

 1) LBR contains invalid data (quite possible)
 2) part of the basic block got paged out
 3) the reported IP isn't part of the basic block (see 1)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Masami Hiramatsu <mhiramat@redhat.com>
Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>
Cc: paulus@samba.org
Cc: eranian@google.com
Cc: robert.richter@amd.com
Cc: fweisbec@gmail.com
LKML-Reference: <20100304140100.619375431@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
2010-03-03 13:12:23 +01:00
committed by Ingo Molnar
parent caff2befff
commit ef21f683a0
5 changed files with 144 additions and 39 deletions
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19
arch/x86/include/asm/perf_event.h
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@@ -136,6 +136,25 @@ extern void perf_events_lapic_init(void);
#define PERF_EVENT_INDEX_OFFSET 0
/*
* Abuse bit 3 of the cpu eflags register to indicate proper PEBS IP fixups.
* This flag is otherwise unused and ABI specified to be 0, so nobody should
* care what we do with it.
*/
#define PERF_EFLAGS_EXACT (1UL << 3)
#define perf_misc_flags(regs) \
({ int misc = 0; \
if (user_mode(regs)) \
misc |= PERF_RECORD_MISC_USER; \
else \
misc |= PERF_RECORD_MISC_KERNEL; \
if (regs->flags & PERF_EFLAGS_EXACT) \
misc |= PERF_RECORD_MISC_EXACT; \
misc; })
#define perf_instruction_pointer(regs) ((regs)->ip)
#else
static inline void init_hw_perf_events(void) { }
static inline void perf_events_lapic_init(void) { }