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Date: Wed, 1 Jul 2009 21:02:09 +0200
From: Frederic Weisbecker <fweisbec@...il.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Mike Galbraith <efault@....de>,
Paul Mackerras <paulus@...ba.org>,
Anton Blanchard <anton@...ba.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Frederic Weisbecker <fweisbec@...il.com>
Subject: [PATCH 1/2] perfcounter: Ignore the nmi call frames in the x86-64 backtraces
About every callchains recorded with perf record are
filled up including the internal perfcounter nmi frame:
perf_callchain
perf_counter_overflow
intel_pmu_handle_irq
perf_counter_nmi_handler
notifier_call_chain
atomic_notifier_call_chain
notify_die
do_nmi
nmi
We want ignore this frame as it's not interesting for instrumentation.
To solve this, we simply ignore every frames from nmi context.
New example of "perf report -s sym -c" after this patch:
9.59% [k] search_by_key
4.88%
search_by_key
reiserfs_read_locked_inode
reiserfs_iget
reiserfs_lookup
do_lookup
__link_path_walk
path_walk
do_path_lookup
user_path_at
vfs_fstatat
vfs_lstat
sys_newlstat
system_call_fastpath
__lxstat
0x406fb1
3.19%
search_by_key
search_by_entry_key
reiserfs_find_entry
reiserfs_lookup
do_lookup
__link_path_walk
path_walk
do_path_lookup
user_path_at
vfs_fstatat
vfs_lstat
sys_newlstat
system_call_fastpath
__lxstat
0x406fb1
[...]
For now this patch only solves the problem in x86-64.
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
arch/x86/include/asm/stacktrace.h | 2 ++
arch/x86/kernel/cpu/perf_counter.c | 8 +++++++-
arch/x86/kernel/dumpstack_32.c | 6 ++++++
arch/x86/kernel/dumpstack_64.c | 22 +++++++++++++++-------
4 files changed, 30 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index f517944..cf86a5e 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -3,6 +3,8 @@
extern int kstack_depth_to_print;
+int x86_is_stack_id(int id, char *name);
+
/* Generic stack tracer with callbacks */
struct stacktrace_ops {
diff --git a/arch/x86/kernel/cpu/perf_counter.c b/arch/x86/kernel/cpu/perf_counter.c
index d4cf4ce..36c3dc7 100644
--- a/arch/x86/kernel/cpu/perf_counter.c
+++ b/arch/x86/kernel/cpu/perf_counter.c
@@ -1561,6 +1561,7 @@ void callchain_store(struct perf_callchain_entry *entry, u64 ip)
static DEFINE_PER_CPU(struct perf_callchain_entry, irq_entry);
static DEFINE_PER_CPU(struct perf_callchain_entry, nmi_entry);
+static DEFINE_PER_CPU(int, in_nmi_frame);
static void
@@ -1576,7 +1577,9 @@ static void backtrace_warning(void *data, char *msg)
static int backtrace_stack(void *data, char *name)
{
- /* Process all stacks: */
+ per_cpu(in_nmi_frame, smp_processor_id()) =
+ x86_is_stack_id(NMI_STACK, name);
+
return 0;
}
@@ -1584,6 +1587,9 @@ static void backtrace_address(void *data, unsigned long addr, int reliable)
{
struct perf_callchain_entry *entry = data;
+ if (per_cpu(in_nmi_frame, smp_processor_id()))
+ return;
+
if (reliable)
callchain_store(entry, addr);
}
diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index d593cd1..bca5fba 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -19,6 +19,12 @@
#include "dumpstack.h"
+/* Just a stub for now */
+int x86_is_stack_id(int id, char *name)
+{
+ return 0;
+}
+
void dump_trace(struct task_struct *task, struct pt_regs *regs,
unsigned long *stack, unsigned long bp,
const struct stacktrace_ops *ops, void *data)
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index d35db59..54b0a32 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -19,10 +19,8 @@
#include "dumpstack.h"
-static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
- unsigned *usedp, char **idp)
-{
- static char ids[][8] = {
+
+static char x86_stack_ids[][8] = {
[DEBUG_STACK - 1] = "#DB",
[NMI_STACK - 1] = "NMI",
[DOUBLEFAULT_STACK - 1] = "#DF",
@@ -33,6 +31,15 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
N_EXCEPTION_STACKS + DEBUG_STKSZ / EXCEPTION_STKSZ - 2] = "#DB[?]"
#endif
};
+
+int x86_is_stack_id(int id, char *name)
+{
+ return x86_stack_ids[id - 1] == name;
+}
+
+static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
+ unsigned *usedp, char **idp)
+{
unsigned k;
/*
@@ -61,7 +68,7 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
if (*usedp & (1U << k))
break;
*usedp |= 1U << k;
- *idp = ids[k];
+ *idp = x86_stack_ids[k];
return (unsigned long *)end;
}
/*
@@ -81,12 +88,13 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
do {
++j;
end -= EXCEPTION_STKSZ;
- ids[j][4] = '1' + (j - N_EXCEPTION_STACKS);
+ x86_stack_ids[j][4] = '1' +
+ (j - N_EXCEPTION_STACKS);
} while (stack < end - EXCEPTION_STKSZ);
if (*usedp & (1U << j))
break;
*usedp |= 1U << j;
- *idp = ids[j];
+ *idp = x86_stack_ids[j];
return (unsigned long *)end;
}
#endif
--
1.6.2.3
--
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