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Subject[PATCH 7/9] x86/perf: Exclude the debug stack from the callchains
Date
Dumping the callchains from breakpoint events with perf gives strange
results:

3.75% perf [kernel] [k] _raw_read_unlock
|
--- _raw_read_unlock
perf_callchain
perf_prepare_sample
__perf_event_overflow
perf_swevent_overflow
perf_swevent_add
perf_bp_event
hw_breakpoint_exceptions_notify
notifier_call_chain
__atomic_notifier_call_chain
atomic_notifier_call_chain
notify_die
do_debug
debug
munmap

We are infected with all the debug stack. Like the nmi stack, the debug
stack is undesired as it is part of the profiling path, not helpful for
the user.

Ignore it.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: "K. Prasad" <prasad@linux.vnet.ibm.com>
---
arch/x86/kernel/cpu/perf_event.c | 9 +++++----
1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index c1bbed1..d35f260 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -2287,7 +2287,7 @@ void callchain_store(struct perf_callchain_entry *entry, u64 ip)

static DEFINE_PER_CPU(struct perf_callchain_entry, pmc_irq_entry);
static DEFINE_PER_CPU(struct perf_callchain_entry, pmc_nmi_entry);
-static DEFINE_PER_CPU(int, in_nmi_frame);
+static DEFINE_PER_CPU(int, in_ignored_frame);


static void
@@ -2303,8 +2303,9 @@ static void backtrace_warning(void *data, char *msg)

static int backtrace_stack(void *data, char *name)
{
- per_cpu(in_nmi_frame, smp_processor_id()) =
- x86_is_stack_id(NMI_STACK, name);
+ per_cpu(in_ignored_frame, smp_processor_id()) =
+ x86_is_stack_id(NMI_STACK, name) ||
+ x86_is_stack_id(DEBUG_STACK, name);

return 0;
}
@@ -2313,7 +2314,7 @@ 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()))
+ if (per_cpu(in_ignored_frame, smp_processor_id()))
return;

if (reliable)
--
1.6.2.3


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