perf_counter: 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@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Anton Blanchard <anton@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1246474930-6088-1-git-send-email-fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 7 deletions

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index d35db5993fd6..54b0a3276766 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