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Date: Thu, 18 Mar 2010 16:05:13 +1100
From: Paul Mackerras <paulus@...ba.org>
To: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
Frederic Weisbecker <fweisbec@...il.com>,
benh@...nel.crashing.org
Cc: linux-kernel@...r.kernel.org, anton@...ba.org,
linuxppc-dev@...abs.org
Subject: [PATCH v2] powerpc/perf_events: Implement
perf_arch_fetch_caller_regs
This implements a powerpc version of perf_arch_fetch_caller_regs.
It's implemented in assembly because that way we can be sure there
isn't a stack frame for perf_arch_fetch_caller_regs. If it was in
C, gcc might or might not create a stack frame for it, which would
affect the number of levels we have to skip.
With this, we see results from perf record -e lock:lock_acquire like
this:
# Samples: 24878
#
# Overhead Command Shared Object Symbol
# ........ .............. ................. ......
#
14.99% perf [kernel.kallsyms] [k] ._raw_spin_lock
|
--- ._raw_spin_lock
|
|--25.00%-- .alloc_fd
| (nil)
| |
| |--50.00%-- .anon_inode_getfd
| | .sys_perf_event_open
| | syscall_exit
| | syscall
| | create_counter
| | __cmd_record
| | run_builtin
| | main
| | 0xfd2e704
| | 0xfd2e8c0
| | (nil)
... etc.
Signed-off-by: Paul Mackerras <paulus@...ba.org>
Acked-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
---
arch/powerpc/include/asm/asm-compat.h | 2 ++
arch/powerpc/kernel/misc.S | 28 ++++++++++++++++++++++++++++
2 files changed, 30 insertions(+)
diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h
index c1b475a..a9b91ed 100644
--- a/arch/powerpc/include/asm/asm-compat.h
+++ b/arch/powerpc/include/asm/asm-compat.h
@@ -28,6 +28,7 @@
#define PPC_LLARX(t, a, b, eh) PPC_LDARX(t, a, b, eh)
#define PPC_STLCX stringify_in_c(stdcx.)
#define PPC_CNTLZL stringify_in_c(cntlzd)
+#define PPC_LR_STKOFF 16
/* Move to CR, single-entry optimized version. Only available
* on POWER4 and later.
@@ -51,6 +52,7 @@
#define PPC_STLCX stringify_in_c(stwcx.)
#define PPC_CNTLZL stringify_in_c(cntlzw)
#define PPC_MTOCRF stringify_in_c(mtcrf)
+#define PPC_LR_STKOFF 4
#endif
diff --git a/arch/powerpc/kernel/misc.S b/arch/powerpc/kernel/misc.S
index 2d29752..b485a87 100644
--- a/arch/powerpc/kernel/misc.S
+++ b/arch/powerpc/kernel/misc.S
@@ -127,3 +127,31 @@ _GLOBAL(__setup_cpu_power7)
_GLOBAL(__restore_cpu_power7)
/* place holder */
blr
+
+#ifdef CONFIG_EVENT_TRACING
+/*
+ * Get a minimal set of registers for our caller's nth caller.
+ * r3 = regs pointer, r5 = n.
+ *
+ * We only get R1 (stack pointer), NIP (next instruction pointer)
+ * and LR (link register). These are all we can get in the
+ * general case without doing complicated stack unwinding, but
+ * fortunately they are enough to do a stack backtrace, which
+ * is all we need them for.
+ */
+_GLOBAL(perf_arch_fetch_caller_regs)
+ mr r6,r1
+ cmpwi r5,0
+ mflr r4
+ ble 2f
+ mtctr r5
+1: PPC_LL r6,0(r6)
+ bdnz 1b
+ PPC_LL r4,PPC_LR_STKOFF(r6)
+2: PPC_LL r7,0(r6)
+ PPC_LL r7,PPC_LR_STKOFF(r7)
+ PPC_STL r6,GPR1-STACK_FRAME_OVERHEAD(r3)
+ PPC_STL r4,_NIP-STACK_FRAME_OVERHEAD(r3)
+ PPC_STL r7,_LINK-STACK_FRAME_OVERHEAD(r3)
+ blr
+#endif /* CONFIG_EVENT_TRACING */
--
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