Re: Fw: Re: [PATCH 1/1] powerpc/perf: Adjust callchain based on DWARF debug info

From: Sukadev Bhattiprolu
Date: Tue Jun 03 2014 - 03:47:44 EST

Jiri Olsa [jolsa@xxxxxxxxxx] wrote:
| On Fri, May 30, 2014 at 05:59:25PM +0200, Jiri Olsa wrote:
| > On Fri, May 30, 2014 at 08:50:19AM -0700, Sukadev Bhattiprolu wrote:
| > > Jiri Olsa [jolsa@xxxxxxxxxx] wrote:
| > > | On Fri, May 16, 2014 at 02:03:33PM -0700, Sukadev Bhattiprolu wrote:
| > > | > Hi Arnaldo, Jiri
| > > | >
| > > | > Do you have any comments on this patch ? Pls let me know if you need
| > > | > me to resend this. The TODO is for a less frequent case and can be
| > > | > addressed independently.
| > > |
| > > | hi,
| > > | I can take it, but it does not apply to my perf/core,
| > > | there're some ARM related unwind changes already:
| > > | git://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
| > > |
| > > | please resend updated patch
| > >
| > > Jiri,
| > >
| > > I resent the patch. Can you please let me know if you have any
| > > comments ?
| > >
| > > https://lkml.org/lkml/2014/5/22/695
| >
| > sry, got distracted.. yep, that one seems looks ok now, I'll queue it
| >
|
| so.. I tried some performance test and looks like this
| adds some considerable penalty also for archs != powerpc
|
| test data:
| $ sudo ./perf record -a -g -F 50000 # perf.data size is ~1.1GB
|
| before your patch:
|
| Performance counter stats for './perf.old report --stdio' (5 runs):
|
| 60,345,248,146 cycles ( +- 0.50% ) âââââ
| 72,766,496,819 instructions # 1.21 insns per cycle ( +- 0.00% ) âââââ
|
| 19.930324523 seconds time elapsed ( +- 1.07% ) âââââ
|
| with your patch:
| 62,559,079,470 cycles ( +- 2.10% ) âââââ
| 72,649,781,930 instructions # 1.16 insns per cycle ( +- 0.00% ) âââââ
|
| 23.355028944 seconds time elapsed ( +- 9.85% ) âââââ
|
|
| I think the issue is following hunk (I havent verified with record/report):
|
| @@ -1300,14 +1301,25 @@ static int machine__resolve_callchain_sample(struct machine *machine,
| return 0;
| }
|
| + /*
| + * Based on DWARF debug information, some architectures skip
| + * some of the callchain entries saved by the kernel.
| + */
| + skip_slot = arch_skip_callchain_idx(machine, thread, chain);
| +
| for (i = 0; i < chain_nr; i++) {
| u64 ip;
| struct addr_location al;
|
| - if (callchain_param.order == ORDER_CALLEE)
| + if (callchain_param.order == ORDER_CALLEE) {
| + if (i == skip_slot)
| + continue;
| ip = chain->ips[i];
| - else
| + } else {
| + if ((int)(chain->nr - i - 1) == skip_slot)
| + continue;
| ip = chain->ips[chain->nr - i - 1];
| + }
|
|
| could you please change this, so it's nop for arch != powerpc
| via #ifdef I guess.. or some other smart way ;-)

I was trying to avoid the #ifdef in the middle of the function.

How about adding a PERF_CONTEXT_IGNORE and doing something like this:

---
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index e3fc8f0..b671abf 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -719,6 +719,8 @@ enum perf_callchain_context {
PERF_CONTEXT_GUEST_KERNEL = (__u64)-2176,
PERF_CONTEXT_GUEST_USER = (__u64)-2560,

+ PERF_CONTEXT_IGNORE = (__u64)-3840,
+
PERF_CONTEXT_MAX = (__u64)-4095,
};

diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
index 729bbdf..8d1417d 100644
--- a/tools/perf/config/Makefile
+++ b/tools/perf/config/Makefile
@@ -48,6 +48,10 @@ ifneq ($(ARCH),$(filter $(ARCH),x86 arm))
NO_LIBDW_DWARF_UNWIND := 1
endif

+ifeq ($(ARCH),powerpc)
+ CFLAGS += -DHAVE_SKIP_CALLCHAIN_IDX
+endif
+
ifeq ($(LIBUNWIND_LIBS),)
NO_LIBUNWIND := 1
else
diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
index 8f84423..333018d 100644
--- a/tools/perf/util/callchain.h
+++ b/tools/perf/util/callchain.h
@@ -176,4 +176,56 @@ static inline void callchain_cursor_snapshot(struct callchain_cursor *dest,
dest->first = src->curr;
dest->nr -= src->pos;
}
+
+#ifdef HAVE_SKIP_CALLCHAIN_IDX
+extern int arch_skip_callchain_idx(struct machine *machine,
+ struct thread *thread, struct ip_callchain *chain);
+static inline
+u64 arch_next_callchain_ip(struct ip_callchain *chain, enum chain_order order,
+ int i, int skip_idx)
+{
+ u64 ip;
+
+ /*
+ * As explained in the arch_skip_callcain_idx() implementation on
+ * Power, some callchain entries are meant to be ignored. If this
+ * is one such entry, return PERF_CONTEXT_IGNORE.
+ */
+ ip = PERF_CONTEXT_IGNORE;
+ if (order == ORDER_CALLEE) {
+ if (i != skip_idx)
+ ip = chain->ips[i];
+ } else {
+ int j = (int)chain->nr - i - 1;
+
+ if (j != skip_idx)
+ ip = chain->ips[j];
+ }
+
+ return ip;
+}
+#else
+static inline
+int arch_skip_callchain_idx(struct machine *machine __maybe_unused,
+ struct thread *thread __maybe_unused,
+ struct ip_callchain *chain __maybe_unused)
+{
+ return -1;
+}
+
+static inline
+u64 arch_next_callchain_ip(struct ip_callchain *chain, enum chain_order order,
+ int i, int skip_idx __maybe_unused)
+{
+ u64 ip;
+
+ if (order == ORDER_CALLEE)
+ ip = chain->ips[i];
+ else
+ ip = chain->ips[chain->nr - i - 1];
+
+ return ip;
+}
+#endif
+
#endif /* __PERF_CALLCHAIN_H */
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 7409ac8..a604ea4 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1288,8 +1288,10 @@ static int machine__resolve_callchain_sample(struct machine *machine,
{
u8 cpumode = PERF_RECORD_MISC_USER;
int chain_nr = min(max_stack, (int)chain->nr);
+ enum chain_order order = callchain_param.order;
int i;
int err;
+ int skip_idx;

callchain_cursor_reset(&callchain_cursor);

@@ -1298,14 +1300,17 @@ static int machine__resolve_callchain_sample(struct machine *machine,
return 0;
}

+ /*
+ * Based on DWARF debug information, some architectures skip
+ * some of the callchain entries saved by the kernel.
+ */
+ skip_idx = arch_skip_callchain_idx(machine, thread, chain);
+
for (i = 0; i < chain_nr; i++) {
u64 ip;
struct addr_location al;

- if (callchain_param.order == ORDER_CALLEE)
- ip = chain->ips[i];
- else
- ip = chain->ips[chain->nr - i - 1];
+ ip = arch_next_callchain_ip(chain, order, i, skip_idx);

if (ip >= PERF_CONTEXT_MAX) {
switch (ip) {
@@ -1318,6 +1323,9 @@ static int machine__resolve_callchain_sample(struct machine *machine,
case PERF_CONTEXT_USER:
cpumode = PERF_RECORD_MISC_USER;
break;
+ case PERF_CONTEXT_IGNORE:
+ /* ignore entry. Eg: based on DWARF debug */
+ break;
default:
pr_debug("invalid callchain context: "
"%"PRId64"\n", (s64) ip);
diff --git a/tools/perf/arch/powerpc/Makefile b/tools/perf/arch/powerpc/Makefile
index 744e629..b92219b 100644
--- a/tools/perf/arch/powerpc/Makefile
+++ b/tools/perf/arch/powerpc/Makefile
@@ -3,3 +3,4 @@ PERF_HAVE_DWARF_REGS := 1
LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/dwarf-regs.o
endif
LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/header.o
+LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/skip-callchain-idx.o
diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
new file mode 100644
index 0000000..a7c23a4
--- /dev/null
+++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
@@ -0,0 +1,266 @@
+/*
+ * Use DWARF Debug information to skip unnecessary callchain entries.
+ *
+ * Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation.
+ * Copyright (C) 2014 Ulrich Weigand, IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+#include <inttypes.h>
+#include <dwarf.h>
+#include <elfutils/libdwfl.h>
+
+#include "util/thread.h"
+#include "util/callchain.h"
+
+/*
+ * When saving the callchain on Power, the kernel conservatively saves
+ * excess entries in the callchain. A few of these entries are needed
+ * in some cases but not others. If the unnecessary entries are not
+ * ignored, we end up with duplicate arcs in the call-graphs. Use
+ * DWARF debug information to skip over any unnecessary callchain
+ * entries.
+ *
+ * See function header for arch_adjust_callchain() below for more details.
+ *
+ * The libdwfl code in this file is based on code from elfutils
+ * (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc).
+ */
+static char *debuginfo_path;
+
+static const Dwfl_Callbacks offline_callbacks = {
+ .debuginfo_path = &debuginfo_path,
+ .find_debuginfo = dwfl_standard_find_debuginfo,
+ .section_address = dwfl_offline_section_address,
+};
+
+
+/*
+ * Use the DWARF expression for the Call-frame-address and determine
+ * if return address is in LR and if a new frame was allocated.
+ */
+static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
+{
+ Dwarf_Op ops_mem[2];
+ Dwarf_Op dummy;
+ Dwarf_Op *ops = &dummy;
+ size_t nops;
+ int result;
+
+ result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);
+ if (result < 0) {
+ pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1));
+ return -1;
+ }
+
+ /*
+ * Check if return address is on the stack.
+ */
+ if (nops != 0 || ops != NULL)
+ return 0;
+
+ /*
+ * Return address is in LR. Check if a frame was allocated
+ * but not-yet used.
+ */
+ result = dwarf_frame_cfa(frame, &ops, &nops);
+ if (result < 0) {
+ pr_debug("dwarf_frame_cfa() returns %d, %s\n", result,
+ dwarf_errmsg(-1));
+ return -1;
+ }
+
+ /*
+ * If call frame address is in r1, no new frame was allocated.
+ */
+ if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 &&
+ ops[0].number2 == 0)
+ return 1;
+
+ /*
+ * A new frame was allocated but has not yet been used.
+ */
+ return 2;
+}
+
+/*
+ * Get the DWARF frame from the .eh_frame section.
+ */
+static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc)
+{
+ int result;
+ Dwarf_Addr bias;
+ Dwarf_CFI *cfi;
+ Dwarf_Frame *frame;
+
+ cfi = dwfl_module_eh_cfi(mod, &bias);
+ if (!cfi) {
+ pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ result = dwarf_cfi_addrframe(cfi, pc, &frame);
+ if (result) {
+ pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ return frame;
+}
+
+/*
+ * Get the DWARF frame from the .debug_frame section.
+ */
+static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc)
+{
+ Dwarf_CFI *cfi;
+ Dwarf_Addr bias;
+ Dwarf_Frame *frame;
+ int result;
+
+ cfi = dwfl_module_dwarf_cfi(mod, &bias);
+ if (!cfi) {
+ pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ result = dwarf_cfi_addrframe(cfi, pc, &frame);
+ if (result) {
+ pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ return frame;
+}
+
+/*
+ * Return:
+ * 0 if return address for the program counter @pc is on stack
+ * 1 if return address is in LR and no new stack frame was allocated
+ * 2 if return address is in LR and a new frame was allocated (but not
+ * yet used)
+ * -1 in case of errors
+ */
+static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
+{
+ int rc = -1;
+ Dwfl *dwfl;
+ Dwfl_Module *mod;
+ Dwarf_Frame *frame;
+ int ra_regno;
+ Dwarf_Addr start = pc;
+ Dwarf_Addr end = pc;
+ bool signalp;
+
+ dwfl = dwfl_begin(&offline_callbacks);
+ if (!dwfl) {
+ pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
+ return -1;
+ }
+
+ if (dwfl_report_offline(dwfl, "", exec_file, -1) == NULL) {
+ pr_debug("dwfl_report_offline() failed %s\n", dwarf_errmsg(-1));
+ goto out;
+ }
+
+ mod = dwfl_addrmodule(dwfl, pc);
+ if (!mod) {
+ pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1));
+ goto out;
+ }
+
+ /*
+ * To work with split debug info files (eg: glibc), check both
+ * .eh_frame and .debug_frame sections of the ELF header.
+ */
+ frame = get_eh_frame(mod, pc);
+ if (!frame) {
+ frame = get_dwarf_frame(mod, pc);
+ if (!frame)
+ goto out;
+ }
+
+ ra_regno = dwarf_frame_info(frame, &start, &end, &signalp);
+ if (ra_regno < 0) {
+ pr_debug("Return address register unavailable: %s\n",
+ dwarf_errmsg(-1));
+ goto out;
+ }
+
+ rc = check_return_reg(ra_regno, frame);
+
+out:
+ dwfl_end(dwfl);
+ return rc;
+}
+
+/*
+ * The callchain saved by the kernel always includes the link register (LR).
+ *
+ * 0: PERF_CONTEXT_USER
+ * 1: Program counter (Next instruction pointer)
+ * 2: LR value
+ * 3: Caller's caller
+ * 4: ...
+ *
+ * The value in LR is only needed when it holds a return address. If the
+ * return address is on the stack, we should ignore the LR value.
+ *
+ * Further, when the return address is in the LR, if a new frame was just
+ * allocated but the LR was not saved into it, then the LR contains the
+ * caller, slot 4: contains the caller's caller and the contents of slot 3:
+ * (chain->ips[3]) is undefined and must be ignored.
+ *
+ * Use DWARF debug information to determine if any entries need to be skipped.
+ *
+ * Return:
+ * index: of callchain entry that needs to be ignored (if any)
+ * -1 if no entry needs to be ignored or in case of errors
+ */
+int arch_skip_callchain_idx(struct machine *machine, struct thread *thread,
+ struct ip_callchain *chain)
+{
+ struct addr_location al;
+ struct dso *dso = NULL;
+ int rc;
+ u64 ip;
+ u64 skip_slot = -1;
+
+ if (chain->nr < 3)
+ return skip_slot;
+
+ ip = chain->ips[2];
+
+ thread__find_addr_location(thread, machine, PERF_RECORD_MISC_USER,
+ MAP__FUNCTION, ip, &al);
+
+ if (al.map)
+ dso = al.map->dso;
+
+ if (!dso) {
+ pr_debug("%" PRIx64 " dso is NULL\n", ip);
+ return skip_slot;
+ }
+
+ rc = check_return_addr(dso->long_name, ip);
+
+ pr_debug("DSO %s, nr %" PRIx64 ", ip 0x%" PRIx64 "rc %d\n",
+ dso->long_name, chain->nr, ip, rc);
+
+ if (rc == 0) {
+ /*
+ * Return address on stack. Ignore LR value in callchain
+ */
+ skip_slot = 2;
+ } else if (rc == 2) {
+ /*
+ * New frame allocated but return address still in LR.
+ * Ignore the caller's caller entry in callchain.
+ */
+ skip_slot = 3;
+ }
+ return skip_slot;
+}

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